Generally, it is the wood screw with fingertip head, thick teeth and hard texture, as well as aluminum alloy and plastic. A special type of self-tapping screw used to open threads in metal holes is called a tap.
Self tapping screws for non-metal or soft metal, do not need to hit the bottom hole and tapping; Self tapping screws are pointed, so as to “self tapping”; Ordinary screws are flat – headed and of the same thickness.
Self tapping screw is to say: drill holes without tapping holes, the screw and the general difference, the head is pointed, the tooth distance is relatively large, and the chip free wire tapping is a bit like, can not tap directly screw in, metal and plastic usually use this method.
It can be consolidated on the material, relying on its own thread, will be consolidated body “tap – drill, squeeze, pressure” out of the corresponding thread, so that it closely with each other