To put it simply, coarse thread is what we often call standard thread, if you do not specify whether it is fine tooth or coarse tooth when purchasing bolts, the default is coarse tooth thread; compared with coarse tooth thread, it is in the same nominal diameter, the pitch per inch is different, that is, the number of teeth is different, the pitch of coarse tooth is large, and the pitch of fine tooth is small. When purchasing coarse tooth bolts, there is no need to specially mark the pitch, while fine tooth bolts must be marked with pitch in order to distinguish them.

The bolt lifting angle of fine thread is relatively small, which is beneficial to bolt self-locking; the cross-section scale of coarse thread per foot is larger, the force is better, and it is more suitable to bear greater tension and impact force. Fine tooth bolts are more suitable for some precision occasions, such as metric pipe fittings of hydraulic system, mechanical transmission parts, thin-walled parts with insufficient strength, machine internals limited by controlled parts and shafts with high self-locking requirements, etc.
Coarse tooth bolts have high strength, good interchangeability, convenient disassembly and assembly, complete standard parts, and have a wide range of applications without special requirements.