First, the self-tapping screws are divided into three categories: wood screws, plastic self-tapping screws, triangular thread screws (the cross section is a triangle).
1. Wood screws are used to fix the workpiece on the wood and directly penetrate.
2, plastic self-tapping screws are generally used for the plastic housing of electrical toys, etc., must be pre-opened.
3. The triangular threaded screw is used for fixing the sheet metal such as iron sheet, and it needs to be pre-opened.
Second, generally refers to the pointed, coarse-toothed, hard-wood screws, also aluminum alloy, plastic. A special self-tapping screw for metal hole tapping is called wire tapping. Self-tapping screws are used for non-metal or soft metal without bottom hole and tapping; self-tapping screws are pointed so that they can be "self-tapping"; ordinary screws are flat and have the same thickness. The self-tapping screw is said: the hole of the drill is a hole that does not need tapping. The screw used is different from the general one. The head is pointed and the tooth distance is relatively large. It is similar to the chipless tapping, and can be directly screwed in without tapping. Metals and plastics usually use this method.
