What is Pitch Diameter?

Among many measurement parameters for threaded parts, pitch diameter is considered to be crucial. 

Some typical thread dimensions which define taps, dies, bolts, and other helically threaded parts include pitch, depth, angle, and major and minor diameters. 

The pitch diameter (also known as the effective diameter) is used to determine whether two threaded parts could be successfully mated together. Properly mated parts will demonstrate equal distance between thread flanks when in contact. Pitch diameter refers to the width of the cylinder as it intersects the midpoint of the major and minor diameters, known as the pitch line.

Pitch diameters are an essential component in determining the compatibility between internally and externally threaded parts – nuts and bolts, for example – and are also used as an important frame of reference for other thread measurements.