Proe thread modification, the teacher said that the nominal diameter of coarse thread modification is the large diameter multiplied by 0.85 (external thread), and the nominal diameter of fine thread modification. There is a simple algorithm for the nominal diameter, that is, directly subtract the pitch from the major diameter of the thread, such as external thread M 10 and pitch 1.5 (coarse teeth), then the base diameter is 10- 1.5=8.5 and external thread M 12.

The external thread pitch of M 10 is 1 (fine thread), and the bottom diameter of the screw is 10- 1 = 9.

As for the types of fine teeth, generally speaking, those smaller than coarse teeth are called fine teeth, and commonly used ones are M8× 1, m/kloc-0 ×1.25, M 12× 1.5 and m1.