Glossary of Fastener Terminology

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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 now 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.

Carbon Steel: Carbon steel is a steel which does not contain any substantial amounts of alloying materials other than carbon.

Case Hardened: A case hardened fastener is a fastener of ferrous material having a surface which has been made harder than the core.

Chamfer Angle: The chamfer angle is the angle of the chamfer measured from the normal to the axis of the fastener and is generally specified in conjunction with either a length or a diameter.

Chip: A chip is a small fragment of metal removed from a surface by cutting with a tool.

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, 2A and 3A 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 tightening torque. Cleveloc is a registered trade name of Forest Fasteners.

Coating: Coating is the application of some material such as metal, organic compound, etc. to the surface of a fastener.

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.

Cold Heading Stock: Cold heading stock is material produced under closely controlled manufacturing and inspection methods so as to be suitable for heading and to be free from those defects causing fractures during heading.

Collar: A collar is a raised ring or flange of material on the head or shank of a fastener.

Commercial Fastener: A commercial fastener is a fastener manufactured to published standards and stocked by manufacturers or distributors. The material, dimensions and finish of commercial fasteners conform to the quality level generally recognized by manufacturers and users as commercial quality.

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.

Comparator: A device for inspecting screw threads and outlines by comparing them with a greatly enlarged standard chart.

Compression Fastener: A compression fastener is a fastener the primary function of which is to resist forces which tend to compress it.

Concentric, Concentricity: Two surfaces of a fastener are concentric when they have a common center of axis. Concentricity is the term used to describe this condition.

Cone Proof Load: 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.

Counterboring: Counterboring is the process of enlarging for part of its depth a hole previously formed and to provide a shoulder at the bottom of the enlarged hole. Special tools called counterbores are generally used for this operation.

Countersink: A countersink is an internal chamfer.

Countersinking: Countersinking is the process of beveling or flaring the end of a hole. Holes in which countersunk head type fasteners are to be used must be countersunk to provide a mating bearing surface.

Cracks: Fractures passing through or across grain boundaries without the inclusion of foreign elements.

Creep Strength: At elevated temperatures metal under stress elongates. This elongation increased with time and temperature. To prevent failure it is often necessary to change to heat resistant materials.

Crest: That surface of the thread which joins the flanks of the thread and is farthest frdm the cylinder or cone from which the thread projects.

Crest Clearance: As in a thread assembly, the distance, measured perpendicular to the axis, between the crest of a thread and the root of its mating thread.

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.

Cut Thread: A cut thread is a thread produced by removing material from the surface with a form cutting tool.

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