Each self tapping screw is composed of three parts: the head, the rod, and the end of the rod. Each self tapping screw has four main elements: head shape, tightening method, thread type, and end form.
1. Head shape
There are various shapes of the head. There are round head (semi round head), flat round head, round head flange (with gasket), flat round head flange (with gasket), pan head, pan head flange (with gasket), countersunk head, semi countersunk head, cylindrical head, spherical cylindrical head, horn head, hexagonal head, hexagonal flange head, hexagonal flange (with gasket) head, etc.
2. Twisting method
The twisting method refers to the method of twisting the head of a screw when installing and tightening it. There are two basic methods: external twisting and internal twisting. Generally speaking, external tightening allows for a greater torque than any form of internal tightening (internal groove). External wrench: hexagonal, hexagonal flange face, hexagonal flange, hexagonal flower shape, etc; Internal wrench: straight groove, cross groove H-type, cross groove Z-type, cross groove F-type, square groove, composite groove, internal spline, internal hexagonal flower shape, internal triangle, internal hexagonal, internal 12 angle, clutch groove, six blade groove, high torque cross groove, etc.
3. Thread type
There are various types of threads, including self tapping threads (wide thread), machine threads (regular thread), dry wall nail threads, fiberboard nail threads, and other special threads. In addition, threads can be divided into single lead (single head), double lead (double head), multi lead (multi head), and high and low pitch double head threads.
4. End form
There are mainly two types of end forms: conical end and flat end. But according to usage needs, grooves, notches, or parts similar to drill bit shapes with cutting functions can be machined at the end of the screw in part. In some standards, there are also different forms of conical or flat ends, such as rounded ends.