The design principles of ISO general-purpose metric screw threads ("M" series threads) are defined in international standard ISO 68-1. Each thread is characterized by its major diameter D and its pitch P.
ISO metric threads consist of a symmetric V-shaped thread. In the plane of the thread axis, the flanks of the V have an angle of 60° to each other.
The outermost 1/8 and the innermost 1/4 of the height H of the V-shape are cut off from the profile.