Glossary of Fastener Terminology

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Basic Size: The basic size is that size from which the limits of size are derived by the application of allowances and tolerances.

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

Bearing Surface: The bearing surface is the supporting or locating surface of a fastener with respect to the part which it fastens (mates). The loading of a fastener is usually through the bearing surface.

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

Bevel: The angle that one surface or line makes with another when they are not at right angles, and the slant or inclination of such a surface or line.

Bihexagon Head: A bolt or screw whose cross section of its head is in the shape of a 12 pointed star.

Black Bolts and Nuts: The word black refers to the comparatively wider tolerances employed and not necessarily to the colour of the surface finish of the fastener.

Blank: A blank is a fastener in some intermediate stage of manufacture.

Body: The body of a threaded fastener is the unthreaded portion of the shank.

Bound Body (Body-Bound or Fitted). A bound body is a body which has a definite interference or extremely small clearance with its mating hole.

Body Diameter. The body diameter s the diameter of the body of a threaded fastener.

Bolt: A bolt is the term used for a threaded fastener, with a head, designed to be used in conjunction with a nut.

Bolt. A bolt is a headed and externally threaded mechanical device designed for insertion through an oversized hole and mated with a nut.

Breakaway Torque: The torque necessary to put into reverse rotation a bolt that has not been tightened.

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

British Standard Brass: A specialist thread form based upon the Whitworth thread and consisting of 26 threads per inch whatever the thread diameter.

Broaching. Broaching is the process of removing metal by pushing or pulling a cutting tool, called a broach, along the surface.

BSF: British Standard Fine. A thread form based upon the British Standard Whitworth form but with a finer thread (more threads per inch for a given diameter). This thread form was first introduced in 1908, the thread form is specified in BS 84: 1956.

BSW: British Standard Whitworth. A thread form developed by Sir Joseph Whitworth in 1841. The thread form has rounded roots and crests, the thread form is specified in BS 84: 1956. This thread form was superceded by the Unified thread in 1948 and then the metric thread form.

Bump Thread: A modified thread profile patented and trade mark of the Bosco Tool Inc. The 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.

Burr. A burr is a small amount of material extending out from the edge of a hole, shoulder, etc. as the result of a machining operation.

(Click on the letters below to browse the glossary terms)

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