The thread of the screw is generally divided into coarse teeth and fine teeth, as well as metric teeth, American teeth, English teeth, German standard, Japanese standard teeth and so on. But in China, we usually use metric teeth.
The so-called coarse thread is a standard thread, which can be found in the national standard of thread. Generally, the screws available from us are coarse thread. Compared with fine thread, coarse thread has high strength.The characteristics of goodinterchangeability are widely used and should be the best choice.
Fine thread is relative to coarse thread, and there are standards to check. For details, please refer to the mechanical design manual. Use standard specifications as much as possible in design. The fine thread has a small space size and good self-locking properties. Most of them are used in places where the force is not large and can be adjusted accurately. For measurement purposes, some situations where threaded connectors are undesirable for use of tools such as oil cup covers, battery covers for metal case LED flashlights, etc. Because the pitch of the fine thread is small, the height of the tooth shape is small, it is easy to mess up the teeth during installation, and the burr has a great influence on the assembly. It must be cleaned. At the same time, the number of disassembly and assembly of fine thread should not be too much.
Coarse strength is high, fine seal is good. The same level ensures that the load is not much different (the fine teeth are slightly higher). When tightening, the preload of the two is close. When the anti-loosening measures are not taken, the anti-loosening effect of the fine thread is better than that of the coarse thread. It is generally used for thin-walled parts and parts with high requirements for vibration resistance. When used for adjustment, fine thread has more advantages. Disadvantages of fine thread: it is not suitable for materials with excessively thick tissue and poor strength. When the tightening force is too large, it is easy to slip the wire.