1. The first phase- ordinary self tapping screw
It is the direct product of early sheet metal screws. So it also known as the "sheet metal screw". It is mainly used in the sheet metal channel to connect heating and ventilation system. When put it into the preformed hole, make the metal materials shift which are close to the holes, and at the same time push the metal material into the space between the screw and thread. As a result, it forms the internal thread connecting with screws. This is the earlist, the most basic and the most widely used tapping screw.
2.The second phase - the self cutting tapping screw
Because the ordinary self tapping screw can form the thread only on the relatively thin and good toughness sheet metal material, it cannot be applied to thick, hard, brittle material and material with the poor deformation ability. Thus, a new type of common tapping screws, the self cutting tapping screw was born.
3. The third phase- the self threading tapping screw
In the early 1950s, engineering and technical personnel of fasteners developed a new generation of tapping screw-- the self threading tapping screw. This kind of screw has threaded rod (including thread) and rod end.
4. The fourth phase - the self drilling tapping screw
The above three phases of self tapping screw have one thing in common in use: it is necessary to work out prefabricated hole in advance nn the fittings. This is also their common weaknesses. So, in the early 1960s, engineers of special custom screw have developed the self drilling tapping screw. This is a kind of tapping screw with the shape of drill at the end
