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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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.
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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.