Thread Terminology

A. FULL DIAMETER SHANK: Matches the major thread diameter. It can be formed either by cutting the thread or rolling it on an extruded blank. Commonly found in machine bolts and cap screws.

B. UNDERSIZED SHANK: Slightly smaller than the major diameter, closer to the pitch diameter. Made by rolling threads on a non-extruded blank. Mostly seen in machine screws.

C. PITCH: The length measured along the screw axis between one thread crest and the next.

D. MAJOR DIAMETER: The largest outside diameter of a screw thread.

E. PITCH DIAMETER: An imaginary diameter lying between the major and minor diameters. It represents the effective size of the screw thread.

F. MINOR DIAMETER: The smallest inside diameter of the screw thread.

LEAD: The forward distance a screw thread moves axially in one complete turn.

CUT THREAD: Threads are made by cutting, leaving the shank equal to the major diameter.

ROLLED THREAD: Threads are formed by rolling the blank between dies, which increases the major diameter compared to the unthreaded shank, unless an extruded blank is used.

THREAD CLASSES:

1A & 1B – Loose fit, suitable for quick or rough assembly.

2A & 2B – Standard fit for most commercial nuts, bolts, and screws.

3A & 3B – Close fit used where precision and high-quality work are required.

4 – Theoretical class rarely used today.

5 – Wrench-fit, mostly used for studs and tapped holes where a strong, semi-permanent fit is needed.

Note: Dimensions shown are for guidance only. Other sizes may also be available or can be custom manufactured on request.