Self-tapping screw is used for non-metal or soft metal, do not hit the low hole and tapping; self-tapping screws are pointed, so as to self-tapping; ordinary screws are flat, consistent thickness. Said: drilling holes without tapping holes, with the general and the different screws, the head is sharp, the teeth from the relatively large, and a bit like a wire-free attack, you can not tap directly into the metal and plastic This method is usually used. It can be solidified material, by its own thread, will be solidified body attack - drill, squeeze, pressure out of the corresponding thread, so that close fit with each other.