Coarse thread

The so-called coarse thread actually refers to standard thread. Unless otherwise specified, the stainless steel screws and other fasteners we usually purchase are coarse threads.

The characteristics of coarse thread are high strength, good interchangeability, and comparable standards. Generally speaking, coarse thread should be the optimal choice;

Compared with fine thread, due to the large pitch and angle of thread rise, the self-locking performance is poor. In vibration environments, anti loosening washers and self-locking devices need to be installed; The advantage is that it is easy to disassemble and assemble, equipped with complete standard parts, and easy to exchange;

When marking coarse threads, it is not necessary to indicate the pitch, such as M8, M12-6H, M16-7H, etc., and they are mainly used for connecting threads.

Fine thread

Fine teeth and coarse teeth are exactly the opposite, and are specified to supplement the special usage requirements that coarse teeth cannot meet. Fine teeth threads also have a pitch series, and the pitch of fine teeth is smaller. Therefore, their characteristics are more conducive to self-locking, anti loosening, and more teeth, which can reduce leakage and achieve sealing effect. In some precision situations, stainless steel screws with fine teeth are more convenient for precise control and adjustment.

The disadvantage is that the tensile value and strength are relatively low compared to coarse teeth, and the thread is prone to damage. It is not recommended to disassemble and assemble it multiple times. The accompanying nuts and other fasteners may be equally accurate, with slight size errors, which can easily cause damage to both screws and nuts.

Fine thread is mainly used in metric fittings of hydraulic systems, mechanical transmission parts, thin-walled parts with insufficient strength, internal parts limited by space, and shafts with high self-locking requirements. When labeling fine thread, the pitch must be indicated to distinguish it from coarse thread.

How to choose coarse and fine threads

Both coarse thread and fine thread screws are used for fastening purposes.

Fine toothed screws are generally used to lock thin-walled parts and parts with high anti vibration requirements. Fine thread has good self-locking performance, therefore it has strong anti vibration and anti loosening ability. However, due to the shallow depth of the thread teeth, its ability to withstand greater tensile force is worse than that of coarse thread.

When no anti loosening measures are taken, the anti loosening effect of fine thread is better than that of coarse thread, and it is generally used for thin-walled parts and parts with high anti vibration requirements.

Fine thread has more advantages when making adjustments. The disadvantage of fine thread is that it is not suitable for application on materials with excessively coarse tissue and poor strength. When the tightening force is too high, it is easy to slip the thread.