Screws can be considered a deep knowledge in the international arena. The specifications of the fixing screws used for each material are different, but there are also some basic rules:

1. There are three types of screw pitch: machine teeth, plastic screws, wood screws or wall screws. The screw pitch is mainly related to the density of the material to be locked. The higher the material density, the smaller the pitch.
1. Coarse teeth in machine teeth refer to standard screws used in ordinary occasions; fine teeth can have different pitches according to different requirements, and they also refer to non-standard screws, which are used in special occasions.

2. The pitch of the plastic screws can also be different. For example, the pitch of soft materials such as PP and PE can be increased, so that it is not easy to slip the teeth; while the denser materials such as POM and PC can use screws with a smaller pitch.

2. There are many kinds of screw head type and groove type, which are generally different according to the appearance and tamper resistance, or other requirements. This is relatively intuitive.

3. The shape of the screw tail is more complicated. However, the more common ones we use are flat tail, pointed tail, grooved, triangular, cone and so on. These shapes mainly have several functions: positioning, tin transfer, self-tapping, self-locking and other functions. Different tail requirements can be selected according to the function.  

Four, self-tapping screws are divided into two categories: plastic and hardware.  

1. Plastics generally use self-tapping, except for some special requirements. However, it should be noted that different plastics use screws with different pitches and tail shapes, especially in some heat and stress conditions. Special attention should be paid.

3. Hardware self-tapping generally uses triangular screws, the pitch is the same as machine screws, triangular screws have the characteristics of self-locking and self-tapping, but generally can not be disassembled repeatedly.