Glossary of Fastener and Fixing Terminology

FASTENER TERMINOLOGY     fastener nomenclature

A full glossary of standard terminology and technical terms used in the fixings and fastener industry. Information links with technical drawings, images and dimensional tables for over 3000 fastener products. Bolts, Nuts, Screws, washers, threaded and unthreaded fastener and fixing products.

Links to further detail to expand and give you a complete picture of the term.

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           GLOSSARY           ALPHA LOCATOR                     

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   U  V  W  X  Y  Z     Number

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A2 STAINLESS STEEL FASTENERS

Stainless steel A2 used in the production of fasteners and fixings is also called type 304 and 18.8 It contains 18% Chromium and 8% nickel.  A2 is an austenitic steel and is non-magnetic. The chromium provides a corrosion and oxidation resistance, however, it can tarnish. Stainless steel A2  property classes for fasteners are 50, soft or 70 cold-worked. 

A4 STAINLESS STEEL FASTENERS

Stainless steel material A4 is also called type 316 and is required for marine conditions where you need more resistance to corrosion. Adding molybdenum (2-3%) to the mix provides this extra resistance.

A4 grade is austenitic, non-magnetic, the molybdenum increases the corrosion resistance to withstand attack from many industrial chemicals and solvents and chlorides.

A4 grade stainless steels come in property classes: 50, soft and 80 high-strength

ACME THREAD

Acme thread is a screw thread having a 29 degree included angle. Used largely for feed and adjusting screws on machine tools. Products

ACORN NUT   

Nut shaped like an acorn it has a hexagon base and a domed top that it prevents contact with the threads, Products.

AEROTIGHT ® NUT   

All metal prevailing torque locking nut. The nut is slotted in two places on the top after the nut has been tapped the slots, are bent slightly inwards and downwards.

When the nut is screwed onto the bolt thread the two slotted parts are forced back to their original position.

Their stiffness causes the nut threads to bind onto the bolt threads and provides prevailing torque locking. Products

AGEING (AGING)

The change in the property of a metal when treated to remove it from an unstable condition. Treatment types are quenching, cold working or hardening.

AIR HARDENING

A process of heat hardening and controlled air cooling; mainly used with tool steels and stainless steel. Modern air-hardening steels are characterised by low distortion during heat treatment because of their high-chromium content. Their machinability is good and they have a balance of wear resistance and toughness 

ALLEN ® 

The generic name for a socket screw

The hexagon socket screw has a long history from cold forming of the first mass-produced socket products in 1910 by William Allen, through to modern day manufacture around the globe.

Allen, acquired by Holo-Krome in 1986 is no longer a force in the socket screw market; like Hoover is to vacuum cleaners the name has become part of the Global fastener language 

ALLOY 

To differentiate from low carbon steels with low or no Alloy content against steels with high Alloy content. Alloys change the performance of the steel in strength, corrosion resistance and other properties demanded by the market.

ALLTHREAD 

Round bar threaded for its full length, also called Studding, Is available in all thread types and grades.  Product

ANAEROBIC ADHESIVE 

An adhesive which hardens in the absence of air, such adhesives are often applied to threads, as the threads tighten the air is excluded.

Primarily used as a thread locker. Products

ANCO® NUTS

The Anco nut is extensively used in the petrochemical industry, it is an all-metal self-locking nut with a stainless steel ratchet pin. A Lok-Mor ® patented nut with a non-breakable Stainless Steel Pin. The nut prevents the removal of coatings, damage to the bolt threads and the unique controlled lock indention ensures consistent locking torque.  Product

ANGLE CONTROLLED TIGHTENING

Tightening procedure in which a fastener is first tightened so that the clamped surfaces are pulled together, it is tightened further by giving the nut an additional measured rotation such as a 1/2 turn or more. 

Frequently bolts are tightened beyond their yield point by this method in order to ensure that a precise preload is achieved.

Using this method, bolts of short length can be elongated too much and the bolt material must be sufficiently ductile to cater for the plastic deformation involved. Because of the bolt being tightened beyond yield, its re-use is limited.

ANNEALING

Heating and controlled cooling of steel to remove stress and changing its ductility, this is a prerequisite to cold forging. 

This process removes internal stresses in the fasteners and makes the material more ductile and pliable. The process consists of heating the fasteners to a selected temperature depending upon specification, followed by a slow and carefully regulated cooling to allow the material to stabilise. 

ANODISE

Anodising (UK)  Anodizing (USA) is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.  More detail

ANSI  American National Standards Institute

The American National Standards Institute is a private non-profit making organisation that oversees the development of fastener product standards in the United States. see standards

ANTI-FRICTION COATING

Anti-friction coatings are dry lubricants consisting of suspensions of solid lubricants, such as graphite, PTFE or molybdenum disulphide in a binder. Anti-friction coatings can be applied to fastener threads to replace metallic coatings such as zinc and cadmium and offer maintenance-free permanent lubrication.

By careful selection of the lubricants, anti-friction coatings can be designed to meet specific applications. The coatings are permanently bonded to the metal surface and provide a lubricating film preventing direct metal to metal contact.

ANTI-SEIZE COMPOUND

This compound is used on the threads of fasteners, It can prevent galling of mating surfaces. Anti-seize compounds are frequently used with stainless steel fasteners to prevent this effect. In some applications it is used to improve corrosion resistance to allow the parts to be subsequently dis-assembled, it can provide a barrier to water penetration since the threads are sealed by the compound. Anti-Seize products provide protection in harsh environments and extreme temperatures, they prevent fretting and galvanic corrosion and can also be used as a running-in lubricant for new equipment.

ASME

Dimensional standards for fasteners, developed by the American Society of Mechanical Engineers. (ASME)   

AUSTENITIC

Austenite steel is tough, non-magnetic and tends to work-harden rapidly when cold worked in steels which are austenitic at ordinary temperatures. 

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BARREL NUT    

An internally threaded screw having a slotted head, used in the furniture industry.   Product

BASIC THREAD PROFILE 

This is the theoretical profile of external and internal threads with no manufacturing tolerance applied.

BEAM CLAMP ®

Fasteners used in steel construction that eliminate the need for drilling, welding and riveting.  Product 

BEARING NUTS

Bearing nuts are also known as slotted Hook nuts and are used to lock bearing onto shafts and shafts onto housings.  Product

BEARING STRESS    

The surface pressure acting on a joint face directly as a result of the force applied by a fastener.

BELLEVILLE WASHER

A Belleville washer, also known as a coned-disc spring, conical spring washer, disc spring, or cupped spring washer, is a type of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic. The Belleville name comes from the inventor Julien Belleville who patented the design in France in 1867  Product

BIFURCATED RIVET  

A small rivet having a split end for securing by spreading the ends called a Bifurcated rivet  Product

BI-HEXAGON HEAD 

Bolt or screw whose cross section of its head is in the shape of a 12 pointed star, also called 12 point bolts and Ferry bolts. Product

BI-LOCK ® NUTS

Centre lock and bi lock nuts have deformed threads in the centre of the nut acting as an all metal prevailing torque thread locking mechanism Product

BINDING HEAD   

Rounded top surface and slightly tapered sides. The bearing surface is flat with annular undercut optional.  

Generally used in electrical and radio work because of its identifying undercut beneath the head, which binds and eliminates fraying of stranded wire. Offers an attractively designed, medium-low head with ordinarily sufficient bearing surface. Not ordinarily recommended as a Phillips Recessed head, generally available slotted, often confused with the Pan Head. Product

BINX® NUT

Binx® nuts have two slots on the head of the nut and are dimensionally no bigger than a standard full nut. The Binx Nut’s design incorporates two opposing cantilevers which lock into the mating part with inward and downward pressure minimising thread wear and enabling the nut to be removed and replaced.  Binx Nuts are also unaffected by minor temperature fluctuations or contaminants. Product

BLACK BOLTS AND NUTS

A traditional term relating to low grade 4.8 and below bolt and nut product that historically would have been black Today the word black refers to the comparatively wider tolerances and not necessarily to the colour of the surface finish of the fastener.  Product

BLIND RIVET

Blind rivets, referred to by the generic name of "pop" rivets. POP® was the original brand name of Tucker in 1938.

Blind rivets are tubular and are supplied with a mandrel through the centre. The rivet assembly is inserted into a drilled hole and a tool is used to draw the mandrel into the rivet. This expands the blind end of the rivet and then the mandrel snaps off. Product

BOLT  

Bolt is the term used for a partially threaded fastener, with a head; designed to be used with a nut. The American term for the same product is Cap Head but this generally only covers hexagon heads.  Detail   Product types

BREAKAWAY TORQUE    

The torque necessary to put the bolt into reverse rotation. a bolt that has not been tightened correctly, the breakaway usually caused by vibration.

BREAK-LOOSE TORQUE   

The torque required to effect reverse rotation when a pre-stressed threaded assembly is loosened.

BRINELL HARDNESS TEST

This test consists of forcing a ball of standard diameter into the specimen being tested under standard pressure, and judging the hardness of the material by the amount of metal displaced. 

Hardness

BRITISH STANDARD BRASS           

Specialist thread form based upon the Whitworth thread and consisting of 26 threads per inch whatever the thread diameter.

BRITISH STANDARD CYCLE THREAD   BSC        

BSC Thread has extra fine threads 26 TPI originally for use on Bicycles and motorcycles. the thread runs at a 60 degree rather than a 55 degree angle. 

BROACHING

Broaching is the process of removing metal by forcing a cutting tool, called a broach, to form a profile, which will duplicate the profile of the broaching tool. It is used for the production of the internal drive for socket screws produced in small volumes.

BSF        

British Standard Fine. A thread form based upon the British Standard Whitworth form but with a finer thread; more threads per inch and has the same thread angle as the BSW and smaller thread depth.

BSF was developed by R E B Crompton and his assistant George Field and was first introduced in 1908, the thread form is specified in BS 84: 1956. Detail

BSI   BRITISH STANDARDS INSTITUTE

The United Kingdom authority for technical standards.  Standards

BSW      WHITWORTH

British Standard Whitworth. A thread form developed by Sir Joseph Whitworth in 1841. The thread form has rounded roots and crests, a thread angle of 55 degrees, the thread form is specified in BS 84: 1956.  Product   Detail 

BUGLE HEAD

Similar to countersunk head with a smooth progression from the shank to the angle of the head, similar to the bell of a bugle. Bugle heads that allows the screw to depress the wood surface without breaking it. Used with Decking and Drywall screws.

BUMP THREAD  

A modified thread profile the Bump thread form has a small projection at the pitch diameter that eliminates the clearance from the thread assembly on both flanks. By doing this it is claimed that resistance to vibration loosening is significantly improved.

BUTTON HEAD

This is an internal socket (Allen) head screw type with a rounded head used in furniture assembly  Product 

CADMIUM ELECTROPLATING      

Coating of threaded fasteners with cadmium can provide the parts with excellent corrosion resistance. The appearance of the coating is bright silver or yellow if subsequently passivated. The friction values associated with this coating are also comparatively low. A chromate conversion coating is frequently applied to the surface to improve corrosion resistance. Cadmium is not frequently used because of the environmental and worker health problems associated with the coating process and should not be used in applications above 250C or when contact with food is possible.  Coaters

CAGE NUTS

Cage  nuts are also called captive and clip nuts, they usually consists of a square nut in a spring steel cage which wraps around the nut. The cage has two wings that when compressed allow the cage to be inserted into the square holes in plate material.  Product

CAP HEAD

An American term for a hexagon bolt also a global term for a socket cap screw

CAP NUT   

Nut shaped like an acorn it has a hexagon base and a domed top that it prevents contact with the threads, Products.

CAPTIVE NUT

Captive nuts capture a washer into the assembly, the washer is free to rotate. Product names are Carp, Combi, SEMs nut.   Product   

CAPTIVE SCREWS 

Where the shank above the threaded portion is undercut lower than the threaded portion. Before threading a washer or another component is located on the shaft and the production of the thread captures the component. This assembly is called a SEMS unit, sems is an abbreviation of asSEMblies; an assembly of a screw and washer.  Screws  Washers

CARBO-NITRIDING 

A process of case hardening an iron base alloy by the simultaneous absorption of carbon and nitrogen through heating in a gaseous atmosphere of suitable composition, followed by cooling at a rate that will produce the desired properties. 

CARP NUT

 Carp nuts capture a washer into the assembly, the washer is free to rotate.    Product   

CARRIAGE BOLT

A bolts originally designed for joining wood to metal, The square neck under the bolt head either fits in a square hole or bites into the sides of a round hole allowing the nut to be tightened. The carriage bolt head is domed with no drive. Product

CASE 

The surface layer of an iron-base alloy which has been made substantially harder than the interior by the process of case hardening. Through hardened and case hardened Dowels are examples of hardened fasteners.

CASE HARDENING 

Carburizing, nitriding or cyaniding and subsequent hardening, by heat treatment, all or part of the surface portions of a piece of iron base alloy. 

CASTLE NUT 

A hexagon nut having a cylindrical portion at the end opposite to the bearing face, with opposed slots in this portion which are parallel to the axis, designed for insertion of a cotter pin to secure the nut in place when used with a body drilled fastener.  Slotted hexagon nuts serve the same objective.  Product  

CE MARKING

CE Marked Fasteners requirements are described in the Construction Products Regulations.  CPR became law in all EU member states from the 1st of July 2013. 

This European regulation replaced the voluntary CPD Construction Products Directive introduced in 1988 and affects all construction products covered by a hEN harmonized European standard  or ETA European Technical Assessment.  more detail

CENTRE (CENTER) LOCK NUTS

Centre lock and bi lock nuts have deformed threads in the centre of the nut acting as an all metal prevailing torque thread locking mechanism Product

CHAMFER POINT

A chamfer point is a truncated cone point, the end of which is flat and perpendicular to the fastener axis. These points on threaded fasteners generally have included angles of 45° to 90° and a point diameter equal to or slightly less than the minor diameter of the thread. The chamfer point is intended to facilitate the ease of entry of fasteners into holes on assembly.

CHARPY TEST 

A test made to determine the notched toughness, or impact strength, of a material. The test gives the energy required to break a standard notched specimen supported at the two ends. 

CHIMNEY NUTS

Spring sheet metal clips used to put a thread on sheet plate, used in conjunction with machine screws   Product

CHIPBOARD SCREW          

A screw designed for use with chipboard also called particle board. Plywood has the potential to feather off in sheaves when extreme weight is placed on the hinges, in contrast, particle board holds the screws in place under similar weight.  Product

CIRCLIP

Circlips hold parts in position on a shaft, designed to fit on a shaft (external) or in a bore (internal) they have eyes to open or close the clip.  Product

CLAMPING FORCE           

The compressive force which a fastener exerts on the joint.

CLASS OF FIT      

The Class of Fit is a measure of the degree of fit between mating internal and external threads. Three main Classes of Fit are defined for metric screw threads :

FINE: This has a tolerance class of 5H for internal threads and 4h for external threads.

MEDIUM: This has a tolerance class of 6H for internal threads and 6g for external threads.

COARSE: This has a tolerance class of 7H for internal threads and 8g for external threads.

For Unified threads, a similar designation as for metric threads is used. The thread classes used are 1A lose, 2A standard and 3A fine for external threads and 1B, 2B and 3B for internal threads.

CLEVELOC ® NUT 

A torque prevailing nut of all metal construction. The collar of the nut is elliptical in cross section and it is this that provides the flexible locking element. The nut is pre-lubricated to reduce the torque needed when tightening and to minimise galling. Product

CLEVIS 

 U-shaped shackle for connecting a rod to a clevis pin. 

CLEVIS PIN 

 A headed dowel pin with a drilled shank that accepts a cotter pin. Used as a fastener where more than temporary holding actions is required. Product

CLINCH NUT 

A nut having a pilot which, after insertion in a hole, is press clinched or staked in place to prevent rotation.  Product

COACH SCREW

A large wood screw with a hexagon or square head know in the USA as a Lag bolt  Product

COARSE PITCH

A thread with a wide pitch. Metric Coarse, Whitworth Coarse, UNC Unified Coarse.

COEFFICIENT OF FRICTION          

A dimensionless number representing the ratio of the friction force to normal force. Typically for threaded connections it is between 0.10 to 0.18 but can vary significantly depending upon the materials used and whether a lubricant has been used. In relation to threaded fasteners, the coefficient of friction can be further sub-divided into the coefficient of friction between the threads and the coefficient of friction under the nut face. There is in general a difference in values between the two coefficients due to the contact surfaces being different. For example, a zinc plated nut on a zinc plated bolt, the thread coefficient of friction would be due to zinc plating contacting zinc plating. The nut face coefficient of friction would be due to zinc plating contacting the joint surface finish.

COILED SPRING PIN

Truly an “engineered-fastener”, the Coiled Pin is available in three “duties” to enable the designer to choose the optimum combination of strength, flexibility and diameter to suit different host materials and application requirements. The Coiled Pin distributes static and dynamic loads equally throughout its cross section without a specific point of stress concentration. Further, its flexibility and shear strength are unaffected by the direction of the applied load, and therefore, the pin does not require orientation in the hole during assembly to maximize performance.

In dynamic assemblies, impact loading and wear often lead to failure. Coiled Pins are designed to remain flexible after installation and are an active component within the assembly. The Coiled Pin’s ability to dampen shock/impact loads and vibration prevents hole damage and ultimately prolongs the useful life of an assembly. Product

COLD HEADING

Cold heading or Cold forging is the process of forming ferrous and non-ferrous materials into specific configurations, without the use of applied heat to assist the formation process

Forging is the process of forming a product by hammering or the displacement of material under force. When the material is forged below the re-crystallisation temperature it is said to be cold forged.   more detail Cold 

COMBINATION HEAD

This is a head with two or more combined drives for example Pozi/Slotted and hexagon/Pozi    Product

COMBI  COMBY NUT

Comby nuts capture a washer into the assembly, the washer is free to rotate.    Product   

COMMINGLING

A term used to describe the undesirable practice of mixing fasteners from different batches that are the same size and grade in the same container. A term extensively used in the USA quality act referring to issues of batch traceability.

CONE POINT

a cone point is a sharp conical point designed to provide locking or aligning functions in the assembly. A point in the form of a cone, commonly having an included angle of 90 degrees or 118 degrees when applied to set screws. Product

CONE PROOF LOAD        

This is an axially applied force applied to a nut when it is seated on a cone-shaped washer which has an included angle of 120 degrees. Failure in this test is usually due to the nut splitting. The intention of the test is to introduce a nut dilation operation which will assess the potential detrimental effects of surface discontinuities. This type of test is sometimes applied to nuts which are intended for high-temperature service.

CONELOC ®  NUT  

The Coneloc® and Stover are all metal prevailing torque type self-locking nut. The locking action is achieved by localised precision deformation of the thread in the cone section on top of the nut. When the nut is tightened onto the bolt, the thread is gripped on the flanks providing the locking action. Product

CONNECTING NUT

A long nut designed to connect threaded rods, allthread and other threaded assemblies together.  Product

COTTER PIN

Also described as a split cotter pin and gets confused with a spring tension pin that is also described as split pin. Split pins are used with castle nuts to lock the nut through a hole in the shank.

 Used as a locking device in clevis pins, castellated nuts and slotted nuts with drilled bolts. Product

COUNTERSUNK HEAD

The countersunk head has a flat top surface and a conical bearing surface with head angles of nominally 60° also angles of 80° and 90° are available. Product

COUPLING NUT

A long nut designed to connect threaded rods, allthread and other threaded assemblies together.  Product

CREEP  

Creep is deformation with time when a part is subjected to constant stress. Metals creep can occur at elevated temperature however with gasket materials it can occur at normal ambient temperatures. Creep resistance is an important property of gasket materials. Gasket materials are designed to flow under stress to fill any irregularities in the flange surface. The amount of creep sustained tends to increase with temperature. . However once the tightening is completed it is important that no further flow occurs since such deformation will lead to a reduction in bolt extension and subsequently the stress acting on the gasket. If this stress is reduced to below a certain minimum, which depends upon the type and construction of the gasket and the operating temperature, a high rate of leakage can be anticipated to occur.

CREST

The surface of the thread that joins the flanks of the thread and is farthest from the cylinder or cone from which the thread projects. The crest of an external thread is at its major diameter while the crest of an internal thread is at its minor diameter.

CROSS DRILLED

A cross-drilled fastener is a fastener having one or more holes in the head or shank, at right angles to, and normally intersecting the axis of the fastener. Detail

CUP POINT 

A point in the form of a cone, commonly having an included angle of 90 degrees, with a conical depression in the end commonly having an included angle of 118 degrees. The contact area is a circular ridge which has considerable holding power with slight penetration, applied to set screws generally.  Product

CUT THREAD

Historic thread manufacture by cutting, Modern threads are rolled. Used where volumes do not exist, where the fastener is large or the fastener is intricate.  Bright

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DACROMET ®

A high performance zinc flake surface coating that can be applied to fasteners. The coating consists of passivated zinc flakes that are stoved onto the metal surface. The coating can be coloured and eliminates the risk of hydrogen embrittlement associated with electroplated metal. Zinc flake

DECOMPRESSION POINT              

The point at which there is zero pressure at the joint interface as a result of forces applied to the joint. If the applied force is increased beyond the decompression point, a gap will form at the interface. Analytically, a criteria of joint failure is often taken as when the applied force on the joint reaches the decompression point. This is because forces acting on the bolt(s) can dramatically increase at this point. Loading beyond this point can also result in fretting at the interface that will lead to bolt tension loss that will subsequently lower the decompression point. This process can continue until bolt failure does occur. The failure can be by fatigue or other mechanism but the underlying cause was loading of the joint beyond the decompression point. It is for this reason that it is frequently taken as a failure criteria in analysis work.

DE-EMBRITTLE

Steel fasteners exposed to hydrogen can fail prematurely at a stress level well below the materials yield strength. Hydrogen embrittlement occurs in fasteners usually as a result of the part being exposed to hydrogen at some time during its manufacturing process or coating process and it can also occur through in-service corrosion.

Electroplating is generally considered to be a major cause of hydrogen embrittlement in steel fasteners due to the absorption of hydrogen during this process. Higher strength steels particularly 12.9 grade are more susceptible to hydrogen embrittlement than lower strength steels, however it is considered that there is no lower strength limit. As a rule of thumb, steels below 10.9 grade are considered to be far less susceptible.  more detail

DESIGN FORM OF THREAD           

The design form of an internal or external thread is the thread form in it's maximum metal condition. It is the same as the basic thread profile except that the thread roots are rounded. If either the internal or external thread form exceeds the design form of the thread profile then a potential interference exists.

DIN

German standards, Deutsches Institut fur Normung. Fastener products are produced to these standards with the standard number after the DIN for example: DIN 912 socket cap screw metric, DIN 933 hexagon screws.  DIN Standards

DIRECT TENSION INDICATORS    

Direct Tension Indicators (DTI's) is a term used to describe load indicating washers. Projections on the face of the washer (usually on the face abutting the bolt head or nut) that deform under loading as the bolt is tensioned. An indication of the tension in the bolt can be made by measuring the gap between the washer face and the nut or bolt head. The smaller the gap - the greater the tension in the bolt. Commonly used in civil rather than mechanical engineering applications.  Product

DISC SPRINGS

Coned-disc spring, conical spring, disc spring, or cupped spring washer, are types of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic.   Product

DOG POINT  

A cylindrical extension, or pilot, of diameter smaller than the minor diameter of the thread, commonly equal to about D/2 in length, with a conical section between it and the thread; usually used as a pilot in assembling or as the end of a set screw projecting into a fairly deep hole or slot.  Product

DOME NUT

Also called an acorn nut, usually hexagon with a sealed end  it has a hexagon base and a domed top that it prevents contact with the threads, Products.

DOUBLE END STUD  

Threaded at both ends with coarse fit threads to take nut assembly.  Product

DOWEL PIN  

Used as a holding pin with chamfered on one end. Extensive range in inch and Metric including pull (extractable) Dowels   Product

DOWEL SCREW  

One end has a Gimlet point, threaded similar to a Lag Bolt. The other end is parallel threaded. Used in joining two wooden members such as a leg to a table top. Product  

DRIVE SCREW  

A piloted, multiple threaded screw with a large helix angle, used for permanent applications. It forms a mating thread as it is hammered or pressed into a prepared hole.  Product

DYNAMIC FRICTION       

Resistance to relative movement of two bodies that are already in motion.

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EFFECTIVE DIAMETER    

This is the diameter of an imaginary cylinder coaxial with the thread, which has equal metal and space widths. It is often referred to as pitch diameter. Sometimes referred to as the simple effective diameter to differentiate from the virtual effective diameter.

EFFECTIVE NUT DIAMETER          

Twice the effective nut radius.

EFFECTIVE NUT RADIUS 

The radius from the centre of the nut to the point where the contact forces, generated when the nut is turned, can be considered to act.

ELASTIC LIMIT 

The maximum load per unit of area that may be applied without producing permanent deformation. It is common practice to apply the load at a constant rate of increase and also measure the increase of length of the specimen at uniform load increments. The point at which the increase in length of the specimen ceases to bear a constant ratio to the increase in load, is called the proportional limit. 

ELECTRO-PLATING     

Electroplating is carried out in a water-based solution containing a chemical compound of the metal to be deposited. The parts to be plated are immersed in the plating bath and an electrical current is passed through which causes the plating metal to precipitate out and to be deposited on the component parts in the plating bath. Coating

ELECTROLESS NICKEL     

A relatively thin, hard coating that can be applied to threads and deposited uniformly. Bright metallic in appearance this coating has excellent resistance to wear and corrosion. Coatings

ELEVATOR BUCKET BOLT

A flat, plain, circular countersunk head bolt with a square neck to prevent rotation.  Product

ELONGATION 

The increase in length of a test specimen after rupture in a tensile test, expressed as a percentage of the original length. 

EMBEDMENT    

Localised plastic metal deformation which occurs in the vicinity of clamped fasteners or in the fastener threads. . Embedding is local metal deformations that occur under the nut face, in the joint faces and in the threads as a result of plastic flattening of the surface roughness. This occurs even when the loading is below the yield point of the bolt or limiting surface pressure of the joint material and is the result of the real area of contact between surfaces being less than the apparent area.

ENGINEERS STUD

A bar threaded at both ends with various fits of thread and combinations of thread length.  Product

ENVIRONMENTALLY ASSISTED CRACKING (EAC)   

A process that can occur with the use of high strength steel fasteners in which crack initiation and growth occurs in the fastener at a comparatively low stress level as a result of interactions that occur with the environment. Hydrogen is suspected of causing EAC in high strength steel fasteners, the hydrogen being produced as a result of chemical reactions (galvanic corrosion in a moist environment) or being present from a plating process that may have been applied to the fastener.

ESCUTCHEON PIN  

A piece generally used to join a plate or shield, to cover or protect softer or more delicate materials or actions.  Product

EXTERNAL FORCE OR LOAD         

Forces exerted on a fastener as a result of an applied loading to the joint.

EXTERNAL THREAD         

A screw thread which is formed on an external cylinder, such as on bolts, screws, and studs.

EYE BOLT  

A bolt having a head in the form of an open or closed anchor ring, or of a flattened and pierced section, with or without a collar or shoulder under the head.   Product

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FAN DISC LOCKING WASHERS

A serrated locking washer with a similar locking mechanism to a shakeproof washer.  Product

FERRY BOLTS

Bolt or screw whose cross section of its head is in the shape of a 12 pointed star, also called 12 point bolts and Ferry bolts. Product

FILLISTER HEAD      

The Fillister head (USA), or Raised Cheese Head.   Product

FINE PITCH

Threads where the pitch is narrower than a coarse pitch. Metric Fine, BSF British Standard Fine, UNF American Unified Fine  Detail

FIT    

Fit is the general term used to signify the range of tolerance parameters. In effect the criteria for allowances and tolerances in the design of mating parts.

The Class of Fit is a measure of the degree of fit between mating internal and external threads. Three main Classes of Fit are defined for metric screw threads :

FINE: This has a tolerance class of 5H for internal threads and 4h for external threads. 

MEDIUM: This has a tolerance class of 6H for internal threads and 6g for external threads. 

COARSE: This has a tolerance class of 7H for internal threads and 8g for external threads.

For Unified threads, a similar designation as for metric threads is used. The thread classes used are 1A lose, 2A standard and 3A fine for external threads and 1B, 2B and 3B for internal threads.

FLANGE BOLT

Flange bolts have a washer flange as an integral part of the head removing the need for a washer and speeding up assembly time.  Product

FLAT HEAD

Flat head is an American term for a Countersunk screw  Product

FLEX LOC ® NUTS

The locking threads of the slotted top press inward against the bolt, lifting the nut upward and causing the remaining threads to bear against the lower surface of the bolt threads. Product

FLOATING TYPE FLANGE JOINT   

A conventional flanged joint in which a gasket is compressed by bolts - the gasket is not rigidly located. Calculation methods such as the ASME code in the USA and the EN1591 code in Europe.

FLUORO-CARBON THREAD COATING       

A low friction coating applied to threads. This type of coating is frequently used to prevent thread fouling when an assembly containing threaded fasteners is painted. Unless masked in some way before painting, electro deposited primers can cover the threads. If this occurs assembly difficulties can result unless the expensive chore of cleaning the threads is completed. A fluoro-carbon thread coating eliminates the need for masking or cleaning since paint will not adhere to the coating. This type of coating can also prevent problems caused by weld splatter obstructing the threads of weld nuts during their placement. Such coatings also have the property of reducing the torque-tension scatter during tightening.

FORGING

Forging is the process of forming a product by hammering or the displacement of material under force. When the material is forged below the re-crystallisation temperature it is said to be cold forged. When worked above the re-crystallisation temperature having been pre-heated, it said to have been hot forged.  more detail Cold  Hot

FRICTION           

Mechanical resistance to the relative movement of two surfaces. There are two main types of friction; STATIC FRICTION and DYNAMIC FRICTION. Typically static friction is greater than dynamic friction.

FRICTION STABILIZERS   

Coating materials used on fasteners with the intention of reducing the scatter in the thread and bearing surface friction coefficients.

FUNDAMENTAL DEVIATION        

An intentional clearance between internal or external thread and the design form of the thread when the thread form is on it's maximum metal condition. For metric threads the fundamental deviation are designated by letters, capitals for internal threads and small letters for external threads. Some tolerance classes have a fundamental deviation of zero. For imperial threads the fundamental deviation is called the allowance.

FUNDAMENTAL TRIANGLE HEIGHT           

The fundamental triangle height is normally designated with the letter H. This is the height of the thread when the profile is extended to a sharp vee form. For 60 degree thread forms such as metric and Unified thread series, H equals 0.866025 times the thread pitch.

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GALLING             

Galling is a severe form of adhesive wear which occurs during sliding contact of one surface relative to another. Clumps of one part stick to the mating part and break away from the surface. It can frequently occur when both the nut and bolt are made from stainless steel and also with high alloy steels, titanium or zinc coated fasteners. In the case of stainless steel using an A4 Nut on an A2 screw can sometimes resolve the problem. Lubrication of threads is the recommended action. Stainless steel

GALVANISE

Applying a coating of molten zinc to a fastener by dipping and then spinning off the excess; under cutting or re-tapping of nut threads is often required  Finish

The term is sometimes confusingly incorrectly applied to zinc electroplating and referred to as electro galvanising.

GEOMET ®

A high performance zinc flake surface coating that can be applied to fasteners. The coating consists of passivated zinc flakes that are bonded on to the metal surface. The coating can be coloured and eliminates the risk of hydrogen embrittlement associated with electroplated steels  Zinc flake

GIMLET POINT       

A gimlet point is a threaded point on a fastener, usually having a point angle of 45° to 50°. It is applied on woodscrews and Type AB self-tapping screws  Points

GRAIN STRUCTURE 

A crystalline structure in metals as observed under the microscope. Cold and Hot forging maintain the grain flow while Bright cut fasteners break the flow.

GRIP LENGTH    

Total distance between the underside of the nut to the bearing face of the bolt head; includes washer, gasket thickness etc.

GRUB SCREW

Term used for slotted non headed setscrews and incorrectly for socket set screws.

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HALF DOG POINT  

The most popular of the Dog points, half as long as a full dog point; used on short screws for the same purposes as the full dog point, but in a shallower hole or slot.  Half Dog  Full Dog

HAMMER DRIVE SCREW

A piloted, multiple threaded screw with a large helix angle, used for permanent applications. It forms a mating thread as it is hammered or pressed into a prepared hole.  Product

HARD JOINT       

A joint in which the plates and material between the nut and bolt bearing surfaces have a high stiffness when subjected to compression by the bolt load. A joint is usually defined as hard if the bolt is tightened to its full torque and it rotates through an angle of 30 degrees or less after it has been tightened to its snug condition.

HARDENED WASHERS    

The force under the head of a bolt or nut can exceed the compressive yield strength of the clamped material at high preloads. If this occurs excessive embedding and deformation can result in bolt preload loss. To overcome this hardened washers under the bolt head can be used to distribute the force over a wider area into the clamped material. A more modern alternative is to use a flange headed nuts and bolts.  Product

 HARDNESS OF STEEL

Hardness grades of steel click for table

HEAD MARKING  

Used to identify the material and manufacturer in a fastener such as a bolt or cap screw. The marking is either raised or indented to specifications.  

HEAT TIGHTENING          

Heat tightening utilises the thermal expansion characteristics of the bolt. The bolt is heated and expands: the nut is indexed (using the angle of turn method) and the system allowed to cool. As the bolt attempts to contract it is constrained longitudinally by the clamped material and a preload results. Methods of heating include direct flame, sheathed heating coil and carbon resistance elements. The process is slow, especially if the strain in the bolt is to be measured, since the system must return to ambient temperature for each measurement. This is not a widely used method and is generally used only on very large bolts.

HELICAL SPRING WASHER            

A split type of spring washer whose purpose is to prevent self loosening of the nut or the bolt. The idea or principle behind the helical spring washer is for one end of the tang of the washer to indent into the fastener (the nut or bolt head) and the other into the joint surface so that any loosening rotation is prevented. Junker in his paper in 1969 on the cause of self-loosening of fasteners concluded that this type of lock washer has limited ability to lock. This type of washer is sometimes called a spring washer. spring lock washer or sometimes a split lock washer. Product

HELI-COIL ® 

Coil of wire used as an insert to accept a screw or bolt and adding holding power by forcing itself between the fastener and the walls of the recess when the fastener is driven in.  

Wire threaded insert is typically used for tapped hole repair or to improve the thread stripping strength of softer metals such as zinc and aluminium. The inserts are assembled into a previously tapped hole using a special driving tool. Thread locking compounds are frequently used to secure the insert if the assembly is subject to vibration.  Product

HEXAVALENT CHROME

Trivalent chromium passivation Cr3 has replaced the toxic Hexavalent chromium on fastener coatings.   

HIGH STRENGTH FRICTION GRIP BOLTS   

Sometimes abbreviated to HSFG bolts. Bolts which are of high tensile strength used in conjunction with high strength nuts, load indicating washers and hardened steel washers in structural steelwork. The bolts are tightened to a specified minimum shank tension so that transverse loads are transferred across the joint by friction between the plates rather than by shear across the bolt shank.  Product

HOLD AND DRIVE BOLTS              

Special bolts that have a tang at the threaded end of the shank. This tang is gripped by the tightening tool during assembly so that the reaction torque is absorbed whilst the nut is tightened from the same side. Such bolts allow what used to have to be done by two men to become a one-man task.

HOLO-KROME

Since its formation in the USA in 1929, Holo-krome has been at the forefront of fastener development and innovation. The company was organized around what was a revolutionary idea at the time the manufacture of socket screws by metal forming or heading rather than machining; later invented a "Cold-Forged" process in which the metal is pre-warmed to improve its plasticity for forming.  Product

HOOK BOLT  

A "bent bolt" having the unthreaded end bent to form a hook, such as a round bend, square bend, right-angle bend, or acute-angle bend hook bolt.  Product

HOOK NUTS

Hook nuts are also known as bearing nuts and are used to lock bearing onto shafts and shafts onto housings.  Product

HOT BOLTING   

This term is used for the completion of maintenance work on a bolted joint when the joint is under loading. This can involve the replacement of individual bolts. There are risks both to the joint itself and to health and safety associated with this technique.

HOT DIP SPUN GALVANISED

Applying a coating of molten zinc to a fastener by dipping and then spinning off the excess; under cutting or retapping of nut threads is often required  Finish

HOT FORGING

Forging is the process of forming a product by hammering or the displacement of material under force. When worked above the re-crystallisation temperature having been pre-heated, it said to have been hot forged.  more detail   Hot

HYDRAULIC TENSIONER

A hydraulic tool used to tighten a fastener by stretching it rather than applying a large torque to the nut. After the fastener has been stretched, the nut is run down the thread to snug up with the joint, the hydraulically applied load is then removed resulting in tension being induced into the fastener.

HYDROGEN EMBRITTLEMENT     

Steel fasteners exposed to hydrogen can fail prematurely at a stress level well below the materials yield strength. Hydrogen embrittlement occurs in fasteners usually as a result of the part being exposed to hydrogen at some time during its manufacturing process or coating process and it can also occur through in-service corrosion.

Electroplating is generally considered to be a major cause of hydrogen embrittlement in steel fasteners due to the absorption of hydrogen during this process. Higher strength steels particularly 12.9 grade are more susceptible to hydrogen embrittlement than lower strength steels, however it is considered that there is no lower strength limit. As a rule of thumb, steels below 10.9 grade are considered to be far less susceptible.  more detail

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IMPACT WRENCH            

A wrench, usually powered by electricity or air, in which repeated blows from little hammers are used to generate torque to tighten fasteners. The torque applied to the fastener depends upon the time and the air pressure applied to the tool (for pneumatic wrenches). The torque applied by an impact wrench to a fastener is influenced by the joint stiffness.

INSTANTANEOUS CENTRE OF ROTATION

The point in space that an eccentrically shear loaded joint rotates about. The deformation and the load sustained by an individual bolt in a bolt group is dependent upon the distance that the bolt is from the instantaneous centre. The direction that the individual bolt force acts is perpendicular to a line joining that bolt to the instantaneous centre.

INTEGRAL FASTENER      

A term used to describe types of fasteners which are highly resistant to vibration loosening or removal. Some types have special thread forms.

INTERNAL THREAD         

A screw thread which is formed in drilled holes, in nuts and threaded inserts.

ISIR  INITIAL SAMPLE INSPECTION REPORT

Submission of a sample batch or a consignment of components for approval.

ISO   INTERNATIONAL ORGANISATION FOR STANDARDISATION

A worldwide federation of national standardisation bodies, their standards are prefixed with the letters ISO.

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J BOLT  

J shaped fastener threaded at one end used in roofing applications. A "bent bolt" having the unthreaded end reverse bent to approximately a semicircle Product

J NUTS

Spring sheet metal clips used to put a thread on sheet plate, used in conjunction with self tapping screws and machine screws   Product

JACK NUTS

Also known as Molly nuts are a threaded inserts. The Jack Nut® (Molly) is a lightweight threaded fastener ideal for use in thin, soft or brittle materials. During setting, the legs of the Jack Nut® collapse to provide a firm anchor on the underside of the material. Jack Nut® is used extensively in vacuum and rotational moulding applications as its flexible grip range can accommodate fluctuation in the moulding process. Product

JAM NUTS          

American term for a lock nuts, two lock nuts are jammed together The term is used for thin nuts used to lock against a second nut. When used in this way the thin nut should be adjacent to the joint surface and tightened against the thick nut. If placed on top of the thick nut the thin nut would sustain loads it was not designed to sustain.

JOINT CONTROL TIGHTENING    

A fastener tightening method which allows a fastener to be tightened to yield. The angle of rotation of the fastener is measured relative to the applied torque, yield being assessed when the slope of the relationship changes to below a certain value. Sometimes called joint controlled tightening.

JOST EFFECT      

The name given to the reduction in the frictional resistance that occurs in a direction different to that in which slip is occurring. This effect is used in many applications including the removal of corks from bottles. If the cork is first rotated the force needed to pull the cork from the bottle is significantly reduced. It is also the fundamental reason why threaded fasteners experience self-loosening. Frictional resistance is first overcome in the transverse direction by slip occurring on the joint resulting in the frictional resistance in the circumferential direction reducing to a small value. The torque acting on the fastener in the loosening direction (as a result of its preload) that when coupled with the Jost Effect results in self-loosening occurring.

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K FACTOR           

The factor in the torque tightening equation: T=KDF where T is the fastener tightening torque in Newton metres, D is the fastener diameter in metres, F is the fasteners preload in Newtons and K is a factor whose value is often taken as 0.2. The formula gives the approximate tightening torque for standard fasteners used under normal conditions. The K factor is also known as the nut factor and the torque coefficient.

KEPS  NUT    

A pre-assembled captive nut and shakeproof washer assembly, the washer is attached to the nut so that it won't fall off. The origin of the word came from ShaKEProof. The s on the end being acquired due to them being purchased in quantities usually greater than one.   Product   

KEY  

A small block or wedge inserted between shaft and hub to prevent circumferential movement. Different types include Woodruff, Gib and Saddle   Product

KEY HEXAGON

Hexagon wrench keys are available as individual 'L' keys, as keys with T handles, also as knife sets and can be produced with ball ends for flexible engagement.  Product 

KNURLED  

A roughened surface produced by contact with a wheel which forces metal above the surface while making indentations below the surface. apply to socket set screw points and wing nut ears  Product   

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LAG BOLT  

A fastener having a square head, with a gimlet or cone point, and a thin, sharp, coarse-pitch thread, designed for insertion in wood or other resilient materials and producing its own mating thread, also known as a coach screw.  Product

 LEFT HAND THREAD         

A screw thread that is screwed in by rotating counter clockwise as opposed to the traditional right hand thread. Fun

LENGTH OF ENGAGEMENT          

The axial distance over which an external thread is in contact with an internal thread.

LINDAPTER ®

Fasteners used in steel construction that eliminate the need for drilling, welding and riveting  Product

LOAD INDICATING WASHERS

Direct Tension Indicators (DTI's) is a term sometimes used to describe load indicating washers. Projections on the face of the washer (usually on the face abutting the bolt head or nut) that deform under loading as the bolt is tensioned. An indication of the tension in the bolt can be made by measuring the gap between the washer face and the nut or bolt head. The smaller the gap - the greater the tension in the bolt. Commonly used in civil rather than mechanical engineering applications.  Product

LOCK BOLTS

LockBolts consist of two parts: a pin, and a collar. The bolt is inserted into one side of the joint material and the collar is placed over the bolt from the other side of the joint material. Access to both sides of the joint is required. An installation tool is used to link the collar to the bolt providing a permanent and vibration resistant fastening.  Product

LOCK NUT          

There are a number of usage's of this term:  

The term is used for thin (or jam) nuts used to lock against a second nut. When used in this way the thin nut should be adjacent to the joint surface and tightened against the thick nut. If placed on top of the thick nut the thin nut would sustain loads it was not designed to sustain.

Lock nuts can also be applied to a nut which provides extra resistance to vibration loosening by either providing some form of prevailing torque, deforming or biting into mating parts when fully tightened; prevailing Torque nuts are also referred to a LOCKING Nuts to differentiate between thin nuts.

LOCK WASHER DISHED

A Belleville washer, also known as a coned-disc spring, conical spring washer, disc spring, or cupped spring washer, is a type of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic. The Belleville name comes from the inventor Julien Belleville who patented the design in France in 1867  Product

LOCK WASHER SERRATED

Washers can be produced with a number of locking elements, serrated locking has been taken to a high level of sophistication.  Products

LOCK WASHER SPRING

A hardened coil wire having a slightly trapezoidal section after forming which functions as a spring take-up device to compensate for developed looseness and the loss of tension between the parts of an assembly and to prevent the nut from turning.  

A split type of spring washer whose purpose is to prevent self loosening of the nut or the bolt. The idea or principle behind the helical spring washer is for one end of the tang of the washer to indent into the fastener (the nut or bolt head) and the other into the joint surface so that any loosening rotation is prevented. Junker in his paper in 1969 on the cause of self-loosening of fasteners concluded that this type of lock washer has limited ability to lock. This type of washer is sometimes called a spring washer. spring lock washer or sometimes a split lock washer. Product 

LOCK WASHER TOOTHED

Are available as a shakepoof washers or fan disc washers both internally and externally toothed.  Fan Disc   Shakeproof

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MACHINE SCREW

Machine screws are the most popular screw, with a full range of heads, drive types and threads. This is a low tensile fastener usually around 4.6 grade, American grade one.  Product 

MAJOR DIAMETER          

This is the diameter of an imaginary cylinder parallel with the crests of the thread; in other words it is the distance from crest to crest for an external thread, or root to root for an internal thread.

MEANSHIFT       

The difference in tightening torque values produced by the same tightening tool on hard and soft joints. A hard joint typically gives a higher torque value than a soft joint. Generally speaking, the lower the meanshift of a tightening tool, the better it will be in achieving a specified torque value irrespective of the joint condition.

METAL TO METAL CONTACT FLANGE JOINT          

A flanged joint in which a gasket is compressed by bolts - the gasket being located in a recess within the joint so that it is compressed by the bolt loads until metal to metal contact occurs. Unlike the FLOATING TYPE FLANGE JOINT, for metal to metal type joints there are no standardised gasket factor definitions, test procedures, nor generally acknowledged calculation procedures available.

MINOR DIAMETER          

This is the diameter of an imaginary cylinder which just touches the roots of an external thread, or the crests of an internal thread.

MODEL ENGINEERS THREAD (M.E.)          

A thread based upon the Whitworth thread form that was established in 1912. A very fine thread (a 3/32 inch thread having 60 tpi for example).

MOLYBDENUM DISULPHIDE        

A solid lubricant that acts as a high pressure resistant film. Can be used by itself as a dry lubricant as well as in with other solid lubricants and in oils and greases. Used in threads, such lubricants act as a separating film to prevent corrosion formation on the thread surface (even under adverse temperature and environmental conditions) ensuring the release of the threaded connection. Such films can also act as friction stabilisers.

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NICKED THREADS            

Nicks or indentations in threads can occur during the manufacturing process, during fastener transportation and barrel plating. In general, nicked thread problems tend to increase as the thread diameter increases and for fine pitches. There are acceptance tests for nicked threads that involve measuring the maximum torque required to drive a GO gauge down the thread. Examples of acceptance tests are SAE J123 and the Ford Motor specification WA990 1993. Nicks and indentations in threads are sometimes referred to as gouges.

NOMINAL DIAMETER     

The diameter equal to the external diameter of the threads.

NORD-LOCK ®

Nord-Lock produce a two piece Locking washer, Nord-Lock washers secure bolted joints with tension instead of friction. It is a high quality product with documented success in many industries worldwide.  Product

NUT  

A metal block or sleeve having an internal thread made to assemble with the external thread on a bolt, screw, or other threaded part. It may be to fastening or to adjust.  

NUT DILATION  

Under load, the wedging action of the threads causes dilation of the nut resulting in an increase in the minor diameter of the nut, and reducing the effective shear areas of both the external and internal threads.

NUT RUNNER    

A torque control fastener tightening tool that is usually powered by compressed air. The design of the tool is such that attempts are made to ensure that the applied torque is independent of joint stiffness.

NYLON FASTENERS  

Non-metallic fasteners made of a Nylon material that has a low dielectric constant and relatively high tensile strength, enabling it to resist high voltage at commercial frequencies. It can also operate at continuous temperatures as high as 120 degrees C.   Detail

NYLOC ® NUT       

A torque prevailing nut that uses a nylon patented insert to provide a locking feature. The nylon insert, it is claimed, helps to seal the bolt thread against seepage of water, oil, petrol, paraffin and other liquids. The nut is covered by UK patent 8028437 and European patent 81303450-1, Nyloc is a registered trade name.

The term Nyloc is also considered generic to the Nylon insert nut family. Product 

NYLON INSERT NUT

A term used to describe a locking nut which has a nylon prevailing torque locking insert. The nylon insert nut family fit into this category both metric and Inch.

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OCTAGON HEAD              

A bolt or screw whose head cross section is a regular polygon with 8 sides or recess is 8 sided. Recess screws can be removed with a square driver.

OIL QUENCH 

A quench from the hardening temperature, in which oil is the cooling medium

OVAL POINT  

A rounded end which is used, particularly for set and adjusting screws, to apply pressure without cutting action.  Product

OVERTAPPING   

Tapping of a thread following a plating or galvanised coating operation so that the thread tolerances comply within specification allowing the internal and external threads to assemble. It is normal practice to overtap the internal rather than the external thread.   Detail

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PALNUT ®

A Palnut is a locking device for nuts made of stamped sheet metal. The palnut is screwed on the bolt on top of an ordinary nut, and has a series of protruding barbs that lock the nut in place when the nut is tightened. The Palnut itself is reusable. A Palnut should not be used as a substitute for a positive locking device such as a prevailing torque nut, castellated or a slotted nut   Product

PAN HEAD

The pan head has a flat under head bearing surface and a shallow oval-shaped head profile similar to a frying pan.  Product

PARABOLT ®

The Parabolt is a through (Thru) bolt for construction fixing into concrete.  Product

PARTICLE BOARD SCREW          

A screw designed for use with particle board also called chipboard. Plywood has the potential to feather off in sheaves when extreme weight is placed on the hinges, in contrast, particle board holds the screws in place under similar weight.  Product

PASSIVATION 

Can refer to the additional process coating applied after electroplating and is the process of enhancing corrosion resistance of zinc and cadmium plated finished by conversion coating with usually a chromium bearing solution. 

 Can also refer to a process for the surface treatment of stainless steels. Material is subjected to the action of an oxidizing solution, usually nitric acid, which augments and strengthens the normal protective oxide film enabling the material to resist corrosive attack. The passivating process also removes foreign substances from the surface which might cause local corrosion . 

PATCH

The term used for nylon or adhesive locking coating on fastener threads.   Nylon    Adhesive

PELLET

This is a nylon pellet inserted into a hole drilled in the fastener threads, in the UK the generic name is Wedglok.  Product

PENTAGON HEAD

A bolt with a pentagon shaped head  Product

PHILIDAS ® NUTS

This is a brand of all metal  prevailing torque locking nut. The nut is slotted in two places on the top, after the nut has been tapped the slots, are bent slightly inwards and downwards. When the nut is screwed onto the bolt thread the two slotted parts are forced back to their original position. Their stiffness causes the nut threads to bind onto the bolt threads and provides  prevailing torque locking.  Product

PHILLIPS ® RECESSED HEAD

A type of screw drive having a cross recess with a wide centre opening, steep walls and a blunt conical bottom. Permits easy and rapid entrance of the 4-winged driver.  more detail

PHOSPHATING CONVERSION COATING             

Phosphate conversion coating is frequently added to bolt threads, to improve corrosion resistance. This type of chemical conversion coating provides a protective passivation layer.  Detail

Phosphating of drawing wire used to produce fasteners assists in lubricating the wire and facilitates cold forming.

PILES    

Term used in structural engineering for the joint plates.

PIPE PLUG  

A short piece of threaded taper or horizontal bar, Slotted, Square Head or Socket head, used to close up one end of a pipe fitting or drainage system.  Socket  Product

PIPE SCREW THREAD  

American Standard pipe threads are tapered 1 inch in 16, or 3/4 inch per foot. They are 60 degree threads, of National form with flat or rounded top and bottom. 

British BSP for parallel and BSPT for tapered 

Metric taper threads show the pitch and then a T for Taper

PITCH   

The nominal distance between two adjacent thread roots or crests. In metric fasteners the distance is measured in mm but for inch fasteners both American and British the threads per inch are counted.

The distance, measured parallel to its axis, between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis.  

PITCH DIAMETER  

On a straight thread, the diameter of the coaxial cylinder, the surface of which would pass through the thread profiles at such points as to make the width of the groove equal to one-half of the basic pitch. On a perfect thread this occurs at the point where the widths of the thread and groove are equal.  

PLAIN FINISH

This term is applied to the finish of fasteners, is used to indicate that the fastener has had no supplementary surface treatment, such as plating and coating, other than being oiled. Sometimes referred to as self-colour.

PLASTIC FASTENERS  

Non-metallic fasteners made of a Nylon and other non-metallic materials that has a low dielectric constant and relatively high tensile strength, enabling it to resist high voltage at commercial frequencies. It can also operate at continuous temperatures as high as 120 degrees C.   Detail

PLATING      

Plating is the executing of a metallic deposit on the surface of the fastener by electrolysis, sometimes referred to as electro plating. Coating

PLOW BOLT

Plow bolts have various shaped heads a square neck followed by a threaded portion.  Product

POOCHING         

Pooching is a term sometimes used to describe the effect of the area immediately surrounding a tapped hole being raised up as a result of the tension from the stud. Tapped holes are often bored out for the first couple of threads to eliminate this problem.

POZIDRIV ®

Four winged drive, with Pozidriv each slot is the result of two machining processes at right angles. The result of this is that the arms of the cross are parallel-sided. more detail

PRELOAD            

The tension created in a fastener when first tightened. Reduces after a period of time due to embedding and other factors.

PREVAILING TORQUE     

The torque required to run a nut down a thread on certain types of nuts designed to resist vibration loosening. The resistance can be provided by a plastic insert, a non-circular head or deformed or coated threads.

PREVAILING TORQUE NUT           

A type of lock nut which has a prevailing torque to assist in preventing self loosening. There are two main categories of prevailing torque nuts, all metal and nylon insert.

All metal torque prevailing nuts generally gain a prevailing torque by distorting the threads of the nut by some means. Aerotight, Anco, Binx, Cleveloc, Centre lock, Flexloc, Philidas, Snep, Staytite, Stover, Toplock and Vargal are all considered all metal locking nuts.

Nylon insert torque prevailing nuts utilise a nylon (or other polymer) insert to achieve a prevailing torque. The nylon insert nut family fit into this category both metric and Inch.

PROOF LOAD     

The proof load of a nut is the axially applied load the nut must withstand without thread stripping or rupture. The proof load of a bolt, screw or stud is the specified load the product must withstand without permanent set.

PROPERTY CLASS             

A designation system which defines the strength of a bolt or nut. For metric fasteners, property classes are designated by numbers where increasing numbers generally represent increasing tensile strengths. The designation symbol for bolts consists of two parts:  

The first numeral of a two digit symbol or the first two numerals of a three digit symbol approximates 1/100 of the minimum tensile strength in MPa.  

The last numeral approximates 1/10 of the ratio expressed as a percentage between minimum yield stress and minimum tensile stress.  

Fasteners with a property class of 8.8 have a minimum tensile strength of 800 MPa and a yield stress of 0.8x800=640 MPa.

The designation system for metric nuts is a single or double digit symbol. The numerals approximate 1/100 of the minimum tensile strength in MPa. For example a nut of property class 8 has a minimum tensile strength of 800 MPa. A bolt or screw of a particular property class should be assembled with the equivalent or higher property class of nut to ensure that thread stripping does not occur.

PRYING

The amplification of an external force acting on a bolt by a lever action which can occur when that force is an eccentric tensile load.

PUSH WASHERS   PUSH NUTS

Push nut is a generic term for Starlock ®  and similar brands of push on fastener for plain shafts. Push nuts eliminate costly threading and grooving operations, facilitate rapid assembly, and once fixed in position, are so secure that they cannot be removed without destruction.  Product

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QUENCH

Quenching, a type of heat treating, the rapid cooling of steel to obtain certain material properties. It can reduce crystallinity and thereby increasing the hardness of alloys. It is most commonly used to harden steel by introducing martensite, in which case the steel must be rapidly cooled. 

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R CLIP

This is a bent wire spring clip shaped in the letter R, can be single or double coil.   Product 

REACH

Registration Evaluation Authorization and restriction of Chemicals regulations.  More Detail

REBAR

Short for reinforcing bar also known as reinforcing steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and hold the concrete in tension. There is a demand for these bars to be threaded at one or both ends.  Detail

RECESSED HEAD  

A screw head, having specially formed indentations or recesses central on the head, into which a suitably formed driver fits, generic names are Pozidriv® and Phillips®  

REDUCED SHANK BOLT  

A bolt whose shank diameter is smaller than the nominal diameter of the bolt, the shank diameter of such a bolt is approximately equal to the effective diameter of the thread.  Product

RELAXATION      

The loss of clamping force in a bolt that occurs typically without any nut rotation occurring. Commonly occurs as a result of embedment but can also be due to gasket creep, metal creep (at elevated temperatures), differential thermal expansion and stress relaxation.

RETAINING RING

A retaining ring is a fastener that holds components or assemblies onto a shaft or in a housing bore when installed in a groove. The exposed portion of the ring acts as a shoulder retaining the component or assembly.  Product

RIBBED NECK BOLTS  

A  bolt with a serrated neck to prevent rotation.  Product

RIGHT HAND THREAD      

A screw thread that is screwed in by rotating clockwise. The majority of screw threads are right handed.

RILSAN

Rilsan is a coating for fasteners approved by the water authorities.  Detail

RIVET SOLID  

A headed metal fastener of some malleable material used to join parts, as metal plates, of structures and machines by inserting the shank through a hole in each piece and forming a head on the headless end. Product  

ROCKWELL HARDNESS TEST 

Forcing a cone-shaped diamond or hardened steel ball into the specimen being tested under standard pressure. The depth of penetration is an indication of the Rockwell Hardness. 

Hardness

ROLLED THREAD              

Rolled threads are formed by plastically deforming a steel blank rather than by cutting. The majority of standard fasteners have their threads formed by rolling. Most threads are rolled before any heat treatment operation.

Significant improvements in fatigue life can be achieved by rolling the thread after heat treatment, this improvement is due to compressive stresses being induced in the roots of the thread. Rolling the thread also generally improves the surface finish which can have a beneficial effect on fatigue life.

ROOT DIAMETER             

Identical to MINOR DIAMETER

ROUND HEAD  

Semi-elliptical top surface and flat bearing surface.  Product

RUN -OUT    

Run-Out is a term frequently interconnected with eccentricity. Normally run-out refers to the amount of run-out with the outside surface of one reference surface of a fastener in comparison with the outside surface of another surface reference on the component. As such, it does include eccentricity, angularity and bow. The amount of run-out is usually expressed in terms of Total Indicator Reading (TIR).

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SAE Specifications  

Standards developed by the Society of Automotive Engineers, USA

SCREW 

Threaded fastener that is designed to be used in conjunction with a pre formed internal thread or alternatively forming its own thread. Historically, it was a threaded fastener with the thread running up to the head of the fastener that has no plain shank, also known in the USA as a tap bolt. The term also applies to fastener or fixing items without a parallel thread such as wood screws, self-tapping screws and other types of fixings. 

SCREW THREAD

A ridge of constant section which is manufactured so that a helix is developed on the internal or external surface of a cylinder.  Thread

SECURITY SCREWS

A screw with a head designed to be driven by a unique driver. Also screws where the driver part of the head breaks off at a predetermined load. see tamper proof  Product

SELF COLOUR

This term as applied to the finish of fasteners, is used to indicate that the fastener has had no supplementary surface treatment, such as plating and coating, other than being oiled. Sometimes referred to as self finish or plain

SELF DRILLING

Self drilling screws tap and drills its own hole during application avoiding the need to do this as a separate operation. Product

SELF-LOCKING  

Where binding action is self-induced on the body of the bolt, screw or nut to keep it rigid and prevent movement and vibration.  

SELF-LOOSENING             

Threaded fasteners can come loose on occasions without human intervention. This loosening can be due to creep, embedding, stress relaxation or the fastener self-rotating (which is often called vibration loosening). Creep, embedding and stress relaxation will generally not completely loosen a fastener, these loosening mechanisms occur without the nut rotating relative to the bolt. The term self-loosening is sometimes used for the nut rotating relative to the bolt without human intervention. It is know that the fastener can self rotate under the action of transverse joint movement that can completely loosen a tightened fastener such that the nut will become detached from the bolt.

SELF TAPPING SCREWS

Tapping screws are normally fully threaded and designed to cut or form their own threads in steel plate on installation.   POINTS

• Type A   Self thread-forming tapping screw having a gimlet point and a thread of relatively coarse pitch, used in punched, or nested holes in metal sheets or in treated plywood; this is the most popular self tapping screw. Product 

• Type B  Also called " Z" . Self thread-forming tapping screw, having a blunt point with tapered threads of moderate pitch, used with punched, drilled or nested holes.   

• Type C  Self thread-forming tapping screw having a blunt point with tapered threads at the end, having UNC or UNF threads and designed for fastening metal sheets.  

• Type D  Also called " EC"   Self thread-cutting tapping screw having the same thread as type C with a fluted end produced at thread rolling or a milled slots produced after thread rolling. 

• Type F   Self thread-cutting tapping screw having the same thread form as type C with a multiple flute tapered end to facilitate tapping.   

• Type FZ  Self thread-cutting tapping screw having the same thread form as type B with a multiple fluted tapered end to facilitate tapping.   

• Type G   Also called "EC"  Self thread-cutting tapping screw having the same thread form as type C with a slot across the end to facilitate tapping in hard materials or deep holes   

• Type H   Also called " DB" or "25" . Self tapping screw having the same thread as a type B with a slot in the end to facilitate tapping in plastics.  

SELF THREADING NUT

Self Threading Nuts have a low height with small exterior dimensions so they are ideal where space is restricted. The thread forming displaces material without making swarf. also called Palnuts®   Product

SEMS NUT

SEMs nuts capture a washer into the assembly, the washer is free to rotate. Product names are Carp, Combi, SEMs nut.   Product   

SEMS SCREW  

A captive screw and washer assembly. A screw or bolt which has a captive washer. The washer is frequently loose on the plain shank of the fastener, the shank diameter being equal to the effective diameter of the thread; the thread being rolled from this diameter. In the 1930's E. C. Crowther was a representative for a company that sold both shakeproof washers and screws. He came up with the idea of placing the washer on the screw before it was thread rolled. The major diameter of the screw being larger than the washer hole prevents it from coming off. The Illinois Tool Works made machines that produced these patented pre-asSEMbled washers and screws. The s at the end of SEMs is thought to have been subsequently picked up because they are not usually purchased individually. In spite of the original patents and trademarks the word SEMS is generally recognised as a generic term applicable to screw and washer assemblies.  Screws 

SEMS WASHER

Washers designed to go with SEMs screws.   Washers

SERRATED FLANGE BOLT

Flange bolts have a washer flange as an integral part of the head removing the need for a washer and speeding up assembly time. Serrations can be added to the flange to produce a locking element.  Product

SERRATED FLANGE NUTS

Flange nuts have an integral washer flanges, Serrations can be added to the flange to produce a locking element   Product

SERRATED LOCKING WASHERS

Washers can be produced with a number of locking elements, serrated locking has been taken to a high level of sophistication.  Products

SET SCREW        

The term is used to describe a full threaded hexagon bolt in the UK described as a tap bolt in the USA  Product

The term is also used to describe a threaded fastener that is typically used to hold a sleeve, collar or gear on a shaft to prevent relative motion. It is a threaded body that normally does not have a head. Unlike most other threaded fasteners it is basically a compression device normally used to generate axial thrust. Various drive types are provided to allow the set screw to be rotated. These types include hexagon socket, fluted socket, screwdriver slot and square head. Various point designs are available (the part of the set screw that rotates against the shaft being secured) and include:

• SET SCREW CONE POINT   Cone - Pointed end, this type of point generates the highest torsional holding power and is typically used for a permanent connection. Product

• SET SCREW CUP POINT    Cup - Hollowed end, is the most commonly used point style. Used when the digging in of the point is not undesirable, leaves a ring mark. Product. 

• SET SCREW DOG POINT    Dog - Flat end with the threads stopping short of the end with the end fitting into a locating hole. Product   Full Dog Point

• SET SCREW FLAT POINT   Flat - Cause little damage to the shaft and are used when frequent adjustment is required. Product

• SET SCREW KNURLED CUP POINT   Knurled cup point is a cup point with knurls' cut in the outside of the cup for improved locking. Product

• SET SCREW OVAL POINT   Oval - Rounded end that is typically used when frequent adjustment is required. The oval end reduces indentation damage. Product 

• SET SCREW THRUST POINT    Thrust point is a rounded point the allows movement at the base of the set screw. Product

• SET SCREW TIP   Tips at the end of the set screw are in various materials and are designed to reduce damage. Product 

• SET SCREW PLUNGER POINT    Set screw containing a spring and ball bearing  Product

SHAKE PROOF LOCKING WASHERS

Similar to a fan disc washer the internal or external teeth lock onto two faces creating a locking action.  Product

SHANK  

The non threaded portion of a bolt between the head and the threaded portion.

SHEAR BOLT

A security tamperproof bolt, the drive snaps off when the required torque has been achieved.  Product

SHEAR NUT  

Can be a fine threaded Thin, Castle or Slotted nut for use with hand shears. 

Can also be a nut that has a head that shears off at an arranged load to create a security fastener. Product

SHEAR STRENGTH 

The stress required to produce fracture in the plane of a cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite although their paths are off set a specified minimum amount. 

SHERARDISING SHERARDIZING  

This coating is intended for medium to long term protection To accommodate these thicknesses on a bolt thread the nut thread must be over-tapped. Details

SHIM WASHER

A thin spacer of sheet metal or washer used for adjusting.  Product

SHOULDER SCREWS        

A threaded fastener with a plain, precision machined, shank that is used for location purposes. They are typically used for pulleys and linkages. Product

SKIDMORE BOLT TENSION CALIBRATOR 

The Skidmore-Wilhelm bolt tension calibrator is a hydraulic load cell used to determine the tension in a bolt or other threaded fastener. The tension in the bolt compresses fluid in a hydraulic cylinder, a pressure gauge connected to the cylinder is then calibrated to read in terms of force rather than pressure.

SLOTTED DRIVE

The head, of a bolt or screw, which has one or more slots across the top to fit a slotted screw driver.  Product

SLOTTED NUT  

A hexagon nut having opposed slots at the end opposite to the bearing face which are perpendicular to the axis, designed for insertion of a cotter pin to secure the nut in place when used with a drilled fastener.  Slotted hexagon nuts serve the same objective as castle nuts.  Product  

SMALLEY

Manufacturer of wavy layered spring washers that act as washers or springs.  Smalley

SNAP RING

Spring retaining rings for bore and shaft the rings are without eyes  Product

SNEP NUT

This all metal locking nut is a prevailing torque nut.   Product

SNUG TORQUE 

The torque required to pull plates together so that direct contact occurs; often used in angle control tightening. The snug torque ensures that metal to metal contact occurs at all the interfaces within the joint. It is only at this point that the required angle of rotation start in order that the bolt is tightened sufficiently. The snug torque is usually determined experimentally on the actual joint.

SOCKET HEAD CAP SCREW           

• METRIC     A screw with a cylinder head, usually with an internal hexagon forged or broached drive. Used where strength is required and is typically made from high strength steel, grade 12.9 in Metric also available in 10.9 and 8.8 grades. Also generically referred to as an Allen screw   Product

• UNIFIED    American INCH 1960 series produced to ANSI B 18.3 with UNC, UNF and number series threads   Product

• UNIFIED    British INCH 1936 series UNC, UNF and number series with changed drive and head sizes     Product

• IMPERIAL  British INCH socket screws are produced with BSF, Whit and BA threads to BS2470   Product

SOCKET BUTTON HEAD SCREW

Internal hexagon drive button head screw generally in grade 10.9 also available with a flange    Button 

SOCKET COUNTERSUNK SCREW  SOCKET FLAT HEAD

Internal Hexagon drive countersunk head screw generally in grades 10.9, 8.8 and branded 12.9; call a flat head in the USA. Available in all thread types   Product

SOCKET LOW HEAD CAP SCREW

Similar to a normal socket cap screw but with a smaller head, available in all thread types. Metric are produced to two standards  DIN7984  DIN6912

SOFT JOINT        

A joint in which the plates and material between the nut and bolt bearing surfaces have a low stiffness when subjected to compression by the bolt load. In such a joint, the bolt (or nut) typically has to be tightened by two or more complete turns, after it has been torqued to the snug condition, before the full tightening torque is achieved. Often the placement of a gasket in a joint results in a soft joint.

SOFT TORQUE   

An alternative name, used by some manufacturers, for snug torque.

SPACERS  

Pieces designed to prevent crushing of sandwich-type and other lightweight structural materials at fastening points.

SPIROLOX ®

A range of specialist retaining rings for shafts and bore.  Product

SPLIT LOCK WASHER

A split type of spring washer whose purpose is to prevent self loosening of the nut or the bolt. The idea or principle behind the helical spring washer is for one end of the tang of the washer to indent into the fastener (the nut or bolt head) and the other into the joint surface so that any loosening rotation is prevented. Junker in his paper in 1969 on the cause of self-loosening of fasteners concluded that this type of lock washer has limited ability to lock. This type of washer is sometimes called a spring washer. spring lock washer or sometimes a split lock washer. Product

SPLIT PIN

Also described as a split cotter pin and gets confused with a spring tension pin that is also described as split pin. Split pins are used with castle nuts to lock the nut through a hole in the shank.

Used as a locking device in clevis pins, castellated nuts and slotted nuts with drilled bolts. Product

SPLIT RIVET  

A small rivet having a split end for securing by spreading the ends also called a Bifurcated rivet  Product

SPRING LOCK WASHER

A hardened coil wire having a slightly trapezoidal section after forming which functions as a spring take-up device to compensate for developed looseness and the loss of tension between the parts of an assembly and to prevent the nut from turning.  

A split type of spring washer whose purpose is to prevent self loosening of the nut or the bolt. The idea or principle behind the helical spring washer is for one end of the tang of the washer to indent into the fastener (the nut or bolt head) and the other into the joint surface so that any loosening rotation is prevented. Junker in his paper in 1969 on the cause of self-loosening of fasteners concluded that this type of lock washer has limited ability to lock. This type of washer is sometimes called a spring washer. spring lock washer or sometimes a split lock washer. Product 

SPRING TENSION PIN

Coiled spring dowels are called spring pins, tension pins, slotted spring pins or roll pins. Spring tension pins are single coil with a single slot, Roll or Spiral ® pins are multi coiled spring tension pins   Product

SPRING TENSION COILED PIN

Truly an “engineered-fastener”, the Coiled Pin is available in three “duties” to enable the designer to choose the optimum combination of strength, flexibility and diameter to suit different host materials and application requirements. The Coiled Pin distributes static and dynamic loads equally throughout its cross section without a specific point of stress concentration. Further, its flexibility and shear strength are unaffected by the direction of the applied load, and therefore, the pin does not require orientation in the hole during assembly to maximize performance.

In dynamic assemblies, impact loading and wear often lead to failure. Coiled Pins are designed to remain flexible after installation and are an active component within the assembly. The Coiled Pin’s ability to dampen shock/impact loads and vibration prevents hole damage and ultimately prolongs the useful life of an assembly. Product

SPRING U  J & CHIMNEY NUTS

Spring sheet metal clips used to put a thread on sheet plate, used in conjunction with self tapping screws and machine screws   Product

SQUARE NECK CARRIAGE BOLT  

A plain, truss or oval head bolt with a square neck to prevent rotation  Product

STAINLESS STEEL

In the fastener world it is described as A2, A4, 18/8, 18/10, 304 and 316 for more detail and corrosion information

STAR LOCK

Push nut is a generic term for Starlock^®  and similar brands of push on fastener for plain shafts. Push nuts eliminate costly threading and grooving operations, facilitate rapid assembly, and once fixed in position, are so secure that they cannot be removed without destruction.  Product

STATIC FRICTION             

Friction at rest; a force is required to initiate relative movement between two bodies - static friction is the force that resists such relative movement. Sometimes referred to as stiction.

STAYTITE

An all metal locking nut using a stainless steel deflecting locking insert   Product

STEP-LOCK BOLT   

The Step-Lock Bolt is a thread form that has been modified to resist vibration loosening. The thread has several horizontal portions (i.e. no lead angle) whose purpose is to prevent torsion being developed in the bolt as a result of the loosening purpose. It is these horizontal portions that are known as steps. The thread form performs well when tested on a transverse vibration test machine. However manufacturing difficulties may prevent its widespread adoption.

STIFFNUT           

A term used to describe a locking nut which has a prevailing torque. The nylon insert nut family fit into this category both metric and Inch.

Also the Prevailing torque all metal nuts of Aerotight, Anco, Binx, Cleveloc, Centre lock, Flexloc, Philidas, Snep, Staytite, Stover, Toplock and Vargal are all considered stiff nuts.

STOVER NUTS

The Stover® and Coneloc® are all metal prevailing torque type self-locking nut. The locking action is achieved by localised precision deformation of the thread in the cone section on top of the nut. When the nut is tightened onto the bolt, the thread is gripped on the flanks providing the locking action. Product

STRENGTH GRADE           

A designation system which defines the strength of a bolt or nut. For metric fasteners, property classes are designated by numbers where increasing numbers generally represent increasing tensile strengths. The designation symbol for bolts consists of two parts:   

The first numeral of a two digit symbol or the first two numerals of a three digit symbol approximates 1/100 of the minimum tensile strength in MPa.   

The last numeral approximates 1/10 of the ratio expressed as a percentage between minimum yield stress and minimum tensile stress.   

Fasteners with a property class of 8.8 have a minimum tensile strength of 800 MPa and a yield stress of 0.8x800=640 MPa. 

The designation system for metric nuts is a single or double digit symbol. The numerals approximate 1/100 of the minimum tensile strength in MPa. For example a nut of property class 8 has a minimum tensile strength of 800 MPa. A bolt or screw of a particular property class should be assembled with the equivalent or higher property class of nut to ensure that thread stripping does not occur.  More detail

STRESS AREA     

The effective cross sectional area of a thread when subjected to a tensile force. It is based upon a diameter which is the mean of the pitch (or effective) and the minor (or root) diameters of the thread. The use of this

diameter stems from the work of E. M. Slaughter in the 1930's. He completed carefully controlled tests using various sizes of standard threads and compared their strength with machined bars made from the same bar of material. He found that this mean diameter gave results that agreed with the tensile test results to within about 3%. The error on the minor and pitch diameters was about 15%. Tests completed subsequent to these by other investigators have also shown that the stress diameter is a reasonable approximation to a thread's tensile strength. 

STRESS RELAXATION       

A significant problem with bolting at high temperatures is a phenomenon known as stress relaxation. Creep occurs when a material is subjected to high temperature and a constant load. Stress relaxation occurs when a high stress is present that is relieved over time; the stress is relaxed with a subsequent reduction in the bolt’s preload. The only way to minimise the effects of stress relaxation is to use materials that have an adequate resistance to it at the product’s operating temperature. The effect of bolt stress relaxation is to reduce the clamp force provided by the bolts; this phenomena alone will not fully loosen a joint.

STRUCTURAL BOLT         

A structural bolt is a heavy hexagon head bolt having a controlled thread length intended for use in structural connections and assembly of such structures as buildings and bridges. The controlled thread length is to enable the thread to stop before the joint ply interface to improve the fastener's direct shear performance. This term is used in civil and structural engineering but is not frequently used in mechanical engineering. Following the introduction of HSFG less structural bolts are used  

STUD    

A fastener which is threaded at both ends with an unthreaded shank in between. One end (which often has a thread tolerance which results in more thread interference) is secured into a tapped hole, the other is used with a nut.  Product

SUPADRIV ®

The Pozidriv® was developed by Phillips to give improved engagement and driver grip to that available from the Phillips® drive (four radial head marks). GKN in the UK subsequently developed the Pozidriv into the Supadriv® (two radial head marks) to provide even more driver engagement, Supadriv® did not, become widely accepted in the market.

SYMMETRICAL THREAD 

A symmetrical thread is one which has both flanks of the thread profile inclined at the same angle.

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TAB WASHERS

A washer with a tab or tabs that can be bent or located to hold the washer in place.  Product

TAMPER PROOF SCREW

A screw with a head designed to be driven by a unique driver. Also screws where the driver part of the head breaks off at a predetermined load. see tamper proof  Product

TAP BOLT

An American term for a fully threaded hexagon head bolt, hexagon set screw.  Product

TAPER PIN

A pin that tapers from the larger end to a smaller end . The taper pin aids in hole alignment. Product

TAPER WASHERS

Square and D shaped with various angles  Product

TAPPING SCREWS

Self tapping screw are generally fully threaded and designed to cut or form their own threads in steel plate on installation various types are shown below.  POINTS

• Type A   Self thread-forming tapping screw having a gimlet point and a thread of relatively coarse pitch, used in punched, or nested holes in metal sheets or in treated plywood; this is the most popular self tapping screw. Product  

• Type B  Also called " Z" . Self thread-forming tapping screw, having a blunt point with tapered threads of moderate pitch, used with punched, drilled or nested holes.    

• Type C  Self thread-forming tapping screw having a blunt point with tapered threads at the end, having UNC or UNF threads and designed for fastening metal sheets.   

• Type D  Also called " EC"   Self thread-cutting tapping screw having the same thread as type C with a fluted end produced at thread rolling or a milled slots produced after thread rolling. 

• Type F   Self thread-cutting tapping screw having the same thread form as type C with a multiple flute tapered end to facilitate tapping.    

• Type FZ  Self thread-cutting tapping screw having the same thread form as type B with a multiple fluted tapered end to facilitate tapping.   

• Type G   Also called "EC"  Self thread-cutting tapping screw having the same thread form as type C with a slot across the end to facilitate tapping in hard materials or deep holes  

• Type H   Also called " DB" or "25" . Self tapping screw having the same thread as a type B with a slot in the end to facilitate tapping in plastics.  

TAYLOR-FORGE METHOD             

A method developed by four engineers of the Taylor-Forge Company in Chicago in the 1930's that subsequently formed the basis of the ASME code for flanged joint design. The assumptions made by the method are now generally regarded as too simplistic. This method gives rise to the m and y gasket factors.

T HEAD BOLT  

Forged Bolt whose head slightly curves in the shape of a "T" . Hence the name "TEE" Head Bolt. Product

TEE NUT PRONGED AND SOLID

Three and four pronged nuts used in the furniture industry, Solid Tee nuts fit into slots or the end of Tee bolts  Product

TEE WELD NUT SLAB BASED

Thread round nuts fixed to a plate with or without welding pips.   Product

TEMPERING

Reheating a quench-hardened or normalized ferrous alloy to a temperature below the transformation range and then cooling at any rate desired.  

TENSILE STRENGTH

The maximum load per unit of original cross-sectional area obtained before rupture of a tensile specimen. 

TENSION WASHERS        

A general name given to spring washers, curved washers, Belleville washers and disc springs. This type of washer provides a relatively low stiffness (compared to the joint stiffness) and can be used to act as a spring take-up with a bolt to prevent movement between parts.

TERMINAL STUD  

A threaded and collared pin having a plain cylindrical section, used as a contact terminal on electrical appliances. Some types are headed instead of collared.  

THREAD CREST  

The top part of the thread. For external threads, the crest is the region of the thread which is on it's outer surface, for internal threads it is the region which forms the inner diameter.

THREAD FLANK 

The thread flanks join the thread roots to the crest.

THREAD FORMING SCREWS

Screws that can produce threads in their mating material, plastic and steel for reusability.  Plastic   Steel

THREAD HEIGHT              

This is the distance between the minor and major diameters of the thread measured radially.

THREAD INSERTS

Wire threaded insert is typically used for tapped hole repair or to improve the thread stripping strength of softer metals such as zinc and aluminium. The inserts are assembled into a previously tapped hole using a special driving tool. Thread locking compounds are frequently used to secure the insert if the assembly is subject to vibration.  Product

Thread inserts for plastic mouldings are a metal integral threaded part of the moulding  Product

Inserts that tap a thread metal thread into plastic parts. Product

THREAD LENGTH             

Length the portion of the fastener with threads.

THREAD-LOCKER

Can be a term used for a number of vibration resistant products but is now usually reserved for thread-locking adhesives. Specifically, a liquid anaerobic adhesive applied to nut or bolt thread, once hardened it fills the inner spaces between the threads to produce a solid plastic of a known shear strength.  Product

THREAD ROOT  

The thread root is the bottom of the thread, on external threads the roots are usually rounded so that fatigue performance is improved.

THREAD RUNOUT           

The portion at the end of a threaded shank which is not cut or rolled to full depth, but which provides a transition between full depth threads and the fastener shank or head.

THUMB SCREW  

A screw with a flattened or roughened head to be turned with thumb and finger.   Product  

THUNDER BOLTS

Designed to be screwed into concrete with a special spaced thread to grip the concrete walls.   Product

TIN/ZINC ALLOY ELECTROPLATING           

Tin/zinc alloy coatings (typically 70% tin and 30% zinc) are applied to threaded fasteners to provide a corrosion resistant coating. One of the advantages of such coatings is that bimetallic corrosion will not occur when placed into contact with such metals as aluminium or steel.

TIPS

Tips at the end of the set screw are in various materials and are designed to reduce damage. Product 

TOLERANCE CLASS          

A combination of tolerance grade and a fundamental deviation which is given to an internal or external thread. A tolerance class for an internal thread when combined with the tolerance class for an external thread gives the class of fit for the mating threads.

TOLERANCE GRADE        

The difference between maximum and minimum metal conditions for a tolerance applied to a screw thread. For metric threads the tolerance grade is given a number.

TOOL POST SCREW

Square headed Tool post screws have a reduced square head and were originally designed to hold cutting tools onto tool posts; they have generally been replaced by the socket head screw.  Product

TOOTH LOCK WASHER

A washer, usually a thin disk with prongs or projections, which is elastically deformed when assembled with a threaded fastener, so that the prongs, on which the pressure is localized, resist loosening of the fastener.   Fan Disc   Shakeproof

TOPLOCK ®

A type of prevailing torque all metal lock nuts similar the Stover ® nut   Product

TORQUE             

A rotational moment; it is a measure of how much twisting is applied to a fastener. The units used to measure torque are in the form of force times length. Usually measured in newton-metres (Nm) if metric units are used or pounds feet (lb-ft) when imperial units are used.

TORQUE MULTIPLIER     

A gearbox used to increase the torque produced by a small hand wrench.

TORQUE WRENCH          

A manual wrench which incorporates a gauge or other method to indicate the amount of torque transferred to the nut or bolt.

TORX HEAD ®

Torx developed in 1967 by Camcar Textron, is a screw head with a 6-point star-shaped pattern. A popular generic name for the drive is star, the official generic name, hexalobular internal drive. This is abbriviated as 6lobe.Torx screws are commonly found on automobiles, motorcycles, hard disk drives, computer systems and consumer electronics. Initially, they were sometimes used in applications requiring tamper resistance or resistance to caming out. Product

TREP ® WASHERS

The TREP® spring washer is made up of three or four smooth, inseparably assembled tapered spring washers that maintain a high level of tension in the screw while conserving considerable elastic energy stored in a small volume. This washer guarantees that the assembly will not loosen in the event of crushing, material expansion, wear or vibration. It compensates for expansion gaps and its elasticity maintains optimal tension in the screws and bolted assembly. Product

TRIM HEADS  

Similar to the 82 degree flat and oval head machine screws except that the size of head for a given size screw is one or two sizes smaller than the regular flat and oval sizes  

TRIVALENT CHROME

A Trivalent chromium passivation Cr3 that has replaced the toxic Hexavalent chromium on fastener coatings.   

TRUSS HEAD  

Low rounded top surface with a flat bearing surface similar to a mushroom head.  

TUBULAR RIVET  

A small rivet having a coaxial cylindrical hole in the headless end, designed for securing by splaying the end.  Product

TURNBUCKLE  

A coupling, threaded right and left or swivelled on one end, for adjustably connecting two rods. Product

TURN OF THE NUT METHOD       

A tightening procedure in which a fastener is first tightened by a pre-selected torque (called the snug torque) so that the clamped surfaces are pulled together, and then is further tightened by giving the nut an additional measured rotation. Frequently bolts are tightened beyond their yield point by this method in order to ensure that a precise preload is achieved. Bolts of short length can be elongated too much by this method and the bolt material must be sufficiently ductile to cater for the plastic deformation involved. Because of the bolt being tightened beyond yield, its re-use is limited.

U  back to the alpha locator

U BOLT

U shaped bent bar fastener threaded at both ends used primarily in suspension and related areas of vehicle construction. Product

U NUT

Spring sheet metal clips used to put a thread on sheet plate, used in conjunction with self tapping screws and machine screws   Product

ULTRASONIC EXTENSOMETER    

An instrument which can measure the change in length of a fastener ultrasonically as the fastener is tightened or measure the length before and after it is tightened).

UNBRAKO

The Unbrako socket screw brand is over 80 years old. Developed in the 1920s, it rapidly became the socket screw of choice for engineers in the US and Britain. After World War II, the product spread to all worldwide market.

UNC      

Unified National Coarse (UNC) is a thread form with a 60 degree flank angle rounded roots and flat crests. For a given diameter it has a larger thread pitch than an equivalent diameter UNF thread. The unified thread is based on inch sizes and was first standardised in 1948 unifying the Whitworth and American standard thread forms.   Thread

UNEF    

Unified National Extra Fine (UNEF) is a Unified thread form with a very fine (small) pitch that are typically used on instruments and parts requiring a fine adjustment.

UNF      

Unified National Fine (UNF) is a thread form with a 60 degree flank angle rounded roots and flat crests. For a given diameter it has a smaller thread pitch than an equivalent diameter UNC thread.   Thread

UNR      

Unified National (UN) thread form with a rounded root contour, applies only to external threads. (The UN thread form has a flat, or optionally, a rounded root contour.) The majority of fasteners with a Unified thread form (UNC UNF) have a rounded root contour i.e. are UNR threads. 

UNIFIED THREAD STANDARDS  

The basic American standards for fastening screw threads as agreed upon by standard bodies of Canada, the United Kingdom, and the United States. They are a complete and integrated system of threads for fastening purposes. Their outstanding characteristic is general interchangeability of threads achieved through the standardization of thread form, diameter-pitch combinations, and limits of size.  Detail

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VARGAL NUT

Spring contained all metal locking nut used in the Railway industry   Product

VICKERS HARDNESS TEST 

The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe the questioned material's ability to resist deformation. 

Hardness

VIRTUAL EFFECTIVE DIAMETER  

The effective diameter of a thread but allowing for errors in pitch and flank angles.

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WASHER  

A washer is a part having a centrally located hole. The washer performs various functions when assembles between the bearing surface of a fastener and the part being attached. Insulation, lubrication, increasing the bearing area over large clearance holes to improved stress distribution are just a few design attributed.   Products     Technical dimensional detail

 WASHER HEAD    

A washer head is a fastener head having a flanged collar under the head of the fastener to provide a bearing surface. Commonly known as a flange head, relative to the generic product type.  Product

WASHER FACE  

A washer face is a circular boss under the head of the fastener, providing a bearing surface. Applicable for a bolt or nut.

WAISTED SHANK BOLT   

A bolt whose diameter is less than the minor diameter of the thread. Frequently the shank of the bolt is 0.9 times the root diameter.

WAVE WASHERS

Wave Spring Washers for pre-loaded bearings in electric motors  Product

WEEE

Regulations for those involved in the manufacture, sale and subsequent disposal of Waste Electrical and Electronic Equipment (WEEE)   Details

WELD NUT

These nuts are very similar to standard square or hex nuts, but have a locating boss and welding projections (lugs, nibs and pips). The bosses help to keep weld spatter out of the thread. Hexagon  Square Round

WELD SCREWS  

Projection welding applied to screws offer a means of providing attached threaded members in sheet metal construction. Welding projections (lugs, nibs and pips) on the head of the screw reduce the amount of current required for surface welding and provide fusion of metal at predetermined points.   Product

WELD STUD  

Stud welding is a process where the stud is welded onto another metal part. The studs are either threaded, un-threaded or tapped.

The different methods of stud welding are:

• Capacitor discharge CD weld studs have a projection tip at the end of the stud. This process uses a direct-current arc from a capacitor when the tip disintegrates, it melts and helps solidify the weld to the base material.

• Spot welding where the stud will have  projections (lugs, nibs and pips) are melted to form the weld.

Product

WHEEL NUTS & BOLTS

Wheel nuts and Bolts are used to hold wheels onto vehicles and also go under the name Lug.  Bolts  Nuts

WHIT OR WHITWORTH  

British Standard Whitworth. A thread form developed by Sir Joseph Whitworth in 1841. The thread form has rounded roots and crests, a thread angle of 55 degrees, the thread form is specified in BS 84: 1956.  Product   Detail 

WING NUT  

One-piece, round threaded nuts with wing lugs for ease of manual assembly. Particularly suited to applications where frequent removal and replacement or adjustment are required. Product  

WING SCREW  

Special screws with projection heads. used in where a finger tightened screw is needed for frequent adjustments or for rapid removal and assembly applications.  Product

WIRE THREAD INSERT    

Threaded insert that is typically used for tapped hole repair or to improve the thread stripping strength of softer metals such as zinc and aluminium. The inserts are assembled into a previously tapped hole using a special driving tool. Thread locking compounds are frequently used to secure the insert if the assembly is subject to vibration.  Product

WOOD SCREW  

A metal screw having a driver head, a gimlet point, and a sharp- crested, coarse pitch thread, for insertion in wood or resilient materials. It produces its own mating thread.  Product

WOODRUFF KEY  

A semi-circular or half-round piece, resting in a circular groove cut in a shaft. Sometimes referred to as a half-moon key. Largely used in machine tool building.  Product

WRENCH KEY HEXAGON

Hexagon wrench keys are available as individual 'L' keys, as keys with T handles, also as knife sets and can be produced with ball ends for flexible engagement.  Product 

X   back to the alpha locator

X GRADE

Grade X is a British imperial fastener grade just under 12.9 grade  Grades

XYLAN

It is a fluoropolymer fastener coating and has a high resistance to solvents, acids, and bases. Xylan

Y    back to the alpha locator

YIELD CONTROLLED TIGHTENING             

Fastener tightening method which allows a fastener to be tightened to yield. The angle of rotation of the fastener is measured relative to the applied torque, yield being assessed when the slope of the relationship changes to below a certain value. Sometimes called joint controlled tightening.

YIELD POINT 

The load per unit of original cross-section area at which a marked increase in the deformation of the specimen occurs without increase in load . Usually calculated from the load determined by the drop of the beam of the testing machine or by use of dividers. 

YIELD STRENGTH 

The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is used for many metals.

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ZINC ELECTROPLATING  

Zinc electroplating is a common way to protect threaded fasteners from the effects of corrosion. Zinc electroplating can be completed in acid chloride, alkaline or cyanide baths. Supplemental coatings are frequently applied to zinc electroplating. These coatings, such as zinc phosphate or chromate conversion, provide a protective passivation layer on the zinc which assists in reducing the corrosion rate.  Detail

ZINC FLAKE COATINGS

Adopted by the automotive industry these coatings are used extensively for automotive fasteners or fasteners used in extreme environments. Geomet®, Dacromet®, Delta protect® are a few of the brand names used.   Zinc Flake

ZINC PHOSPHATE CONVERSION COATING             

Zinc phosphate conversion coating is frequently added to zinc electroplated parts, such as bolt threads, to improve corrosion resistance. This type of chemical conversion coating provides a protective passivation layer on the zinc improving its corrosion resistance.  Detail

ZINC/COBALT ALLOY ELECTROPLATING  

This coating is similar to zinc electroplating completed in an acid chloride bath - a small amount of cobalt (typically about 1%) is added to increase the plating speed.

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12 POINT BOLTS AND NUTS

Bolt or screw whose cross section of its head is in the shape of a 12 pointed star, also called 12 point bolts. Product

18/8 STAINLESS STEEL FASTENERS

18.8 is specified for British Inch it is equivalent to Stainless steel A2 is specified for metric fasteners, American Inch fasteners use the equivalent 304 stainless material specification. It contains 18% Chromium and 8% nickel and is an austenitic steel and is non-magnetic. The chromium provides a corrosion and oxidation resistance, however it can tarnish. 

18/10 STAINLESS STEEL FASTENERS

Contains 18% Chromium and 10% nickel and is an austenitic steel. The chromium provides a corrosion and oxidation resistance, however it can tarnish. 

304 STAINLESS STEEL FASTENERS

Stainless steel A2 is specified for metric fasteners, American Inch fasteners use the equivalent 304 stainless material specification and 18.8 for British Inch.  It contains 18% Chromium and 8% nickel and is an austenitic steel and is non-magnetic. The chromium provides a corrosion and oxidation resistance, however it can tarnish. 

316 STAINLESS STEEL FASTENERS

Stainless steel material A4 is also called type 316 and is required for marine conditions where you need more resistance to corrosion. Adding molybdenum (2-3%) to the mix provides this extra resistance.

316 is austenitic, non-magnetic, the molybdenum increases the corrosion resistance to withstand attack from many industrial chemicals and solvents and chlorides.