General structure of self-tapping screws

Each self-tapping screw is composed of three parts: the head, the shank and the end of the shank. The composition of each self-tapping screw has four major elements: head shape, wrenching method, thread type, and end form.
1. Head shape
The head shape varies. There are round head (semi-round head), oval head, round head flange (with pad), oval head flange (with pad), pan head, pan head flange (with pad), countersunk head, semi-countersunk head, cylindrical head, spherical cylindrical head, horn head, hexagonal head, hexagonal flange head, hexagonal flange (with pad) head, etc.
2. Wrenching method
The wrenching method refers to the way of twisting the screw head when installing and tightening the screw. The basic methods are external wrenching and internal wrenching. Generally speaking, external wrenching allows a larger torque than any form of internal wrenching (inner groove). External wrench: hexagon, hexagonal flange, hexagonal flange, hexagonal flower shape, etc.; internal wrench: slot, cross slot H type, cross slot Z type, cross slot F type, square slot, compound slot, internal spline, internal hexagonal flower shape, internal triangle, internal hexagon, internal 12 angle, clutch slot, six blade slot, high torque cross slot, etc.
3. Thread types
There are many types of threads, including self-tapping threads (wide pitch threads), machine threads (ordinary threads), drywall screw threads, fiberboard screw threads, and some other special threads. In addition, threads can be divided into single lead (single start), double lead (double start), multi-lead (multi-start) and high and low pitch double start threads.
4. End form
The end forms are mainly cone end and flat end. However, according to the needs of use, the screw-in part of the end can be processed with grooves, grooves, cuts or parts similar to drill bit shapes with cutting functions. In some standards, there are also different forms such as round head ends, which are also cone ends or flat ends.