C... Glossary of Fastener and Fixing Terminology

 cadmium electroplating coatings with cage nuts and cap heads. cap-nut-captive-nut-captive-screws-carbo-nitriding-carp-nut-carriage-bolt-case-case-hardening-castle-nut-ce-marking-centre-(center)-lock-nuts-charpy-test-chamfer-point-chipboard-screw-circlip-clamping-force-class-of-fit-cleveloc-nut -clevis-clevis-pin-clinch-nut-coach-screw-coarse-pitch-coefficient-of-friction-cold-heading



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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 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


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


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


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


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


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


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


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.


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


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 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 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


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.


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. 


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


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


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


The compressive force which a fastener exerts on the joint.


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.



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


U-shaped shackle for connecting a rod to a 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


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


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


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


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.


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 


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


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


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


A USA 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.


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


This is an axial 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.


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


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


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


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


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


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.


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.


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


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


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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cadmium electroplating coatings with cage nuts and cap heads. cap-nut-captive-nut-captive-screws-carbo-nitriding-carp-nut-carriage-bolt-case-case-hardening-castle-nut-ce-marking-centre-(center)-lock-nuts-charpy-test-chamfer-point-chipboard-screw-circlip-clamping-force-class-of-fit-cleveloc-nut -clevis-clevis-pin-clinch-nut-coach-screw-coarse-pitch-coefficient-of-friction-cold-heading