Threads - Key Terms Used

These common terms are mainly used when we sell to customers in the engineering industry, but we thought it might be useful to write up a quick guide anyway!

THREADS - KEY TERMS

Thread Pitch

The distance between two individual threads, usually expressed in millimetres. A fine thread has a lower pitch than a coarse thread.

TPI

Thread per inch count. This term means the number of threads present within a radial measurement along the fastener of one inch.

THREAD PER INCH (TPI)

Thread Angle

The angle between two thread flanks. Most threads in common use today have a thread angle of 55 or 60 degrees.

Crest

The top of the thread – the most prominent part.

Root

The bottom of the valley between two threads.

Thread Flank

The straight side of the thread that connects the root to the crest.

Diameter

The diameter across the threads when measured from the crest of the threads. The actual correct term for this measurement is major diameter. (The minor diameter is the measurement from root to root).

These are the terms that you will most probably come across when researching various threads. For further information about the different types of threads in use please read our guide to different thread types found on UK fasteners.