General thread has coarse teeth and fine teeth, the same nominal diameter can have a variety of pitch, in which the larger pitch is called coarse thread, the other are fine thread.

Coarse thread, that is to say, the standard thread, in the thread of the national industry standards can be found, general people outside can buy screw bolts are coarse thread, and fine thread contrast, coarse thread with high strength, tolerance fit good characteristics are widely used, should be used as the optimal selection.

Fine thread is relativistic coarse thread, there are standards to check, can actually see the mechanical design manual.Design as far as possible will use the standard specifications, fine thread of interior space size small, self-locking, most used to pressure is not big, can accurately adjust the region, such as all kinds of optical glasses stationary equipment, instrument equipment such as vernier caliper used for precise measurement of the main USES, some with threaded connection and don't expect the status of the application of special tools such as oil lid, metal case led flashlight rechargeable battery cover these.Because the pitch of fine thread is small, the ratio of height to width of screw teeth is small, it is very easy to appear in the installation of disorderly teeth can not be out of the situation, vibration line is very harmful to the assembly line, must be clean.In addition, fine thread removal frequency is not suitable for excessive.

Second, the strength of thick teeth, fine teeth sealing good.Fine thread and coarse thread screw in the main purposes are all for tighten, fine thread lock screws are used for thick wall parts and parts for vibration isolation is relatively high. Fine thread self-locking feature, and resistance to vibration of fastening work ability is strong, but because of the thread depth is shallow, take more applied work less well than coarse thread. The strength of the fine thread is lower than the strength of the standard thread (coarse thread), standard thread is actually USES such as strength standard, the standard has the strength of the nut its thickness specification, with the strength of the screw is the same, from the perspective of strength, that design is the most effective.Therefore, standard thread is the most common application.However, it is also a defect, which means that the self-locking property is less than that of the fine thread, so a spring washer or other self-locking device must be modified in areas with strong vibration.