Difference Between Coarse Thread And Fine Thread

Coarse thread:

No need to mark the pitch, such as M8, M12-6H, M16-7h, etc., mainly used for connecting threads. Compared with fine thread, due to the large pitch, the thread angle is also large, the self-locking property is poor, and it is generally used with spring washers: the pitch is large, the tooth profile is also deep, and the strength of the main body is greatly reduced. The advantage is that it is easy to disassemble and assemble, and the standard parts are complete and easy to interchange.

Fine thread:

The pitch must be marked to show the difference from the coarse thread. The characteristics are exactly the opposite of the coarse thread. It is stipulated to supplement the special use requirements that the coarse thread cannot meet. The fine thread also has a pitch series, which is mainly used in metric pipe fittings of hydraulic systems, mechanical transmission parts, thin-walled parts with insufficient strength, machine internal parts with space restrictions, and shafts with high self-locking requirements.

The coarse thread has high strength and the fine thread has good sealing. The same level of guaranteed load is not much different (the fine thread is slightly higher). When used for tightening, the preload of the two is close. When no anti-loosening measures are taken, the anti-loosening effect of fine thread is better than that of coarse thread. It is generally used for thin-walled parts and parts with high vibration resistance requirements.
When used for adjustment, fine thread has more advantages. Disadvantages of fine thread: It is not suitable for use on materials with excessively coarse tissue and poor strength. When the tightening force is too large, it is easy to slip.

Fine thread and coarse thread screws are both used for fastening. Fine thread screws are generally used to lock thin-walled parts and parts with high vibration resistance requirements. Fine thread has good self-locking performance, so it has strong anti-vibration and anti-loosening ability, but due to the shallow depth of the thread teeth, its ability to withstand greater tension is worse than that of coarse thread. The strength of fine thread is lower than that of standard thread (coarse thread). Standard thread actually adopts the principle of equal strength, that is, the strength of the standard nut thickness size is equal to the strength of the screw. From the perspective of strength, such a design is the most reasonable.

1. Application of coarse thread

The coarse thread series (M/UNC/UNRC) is generally used for mass production of threaded fasteners, such as bolts, screws, nuts, etc. It has unique advantages in situations where rapid assembly or disassembly is required and where rust and damage are likely to occur. However, its self-locking property is not as good as that of fine and ultra-fine threads.

2. Application of fine thread

The fine thread series (MF/UNF/UNRF) is usually used in situations where fasteners require higher strength. Since fine threads have shallower teeth and larger thread diameters than coarse threads, they have higher thread strength than coarse threads of the same nominal specification. In addition, fine threads can be used for fine-tuning.

3. Application of ultra-fine threads

The ultra-fine thread series (UNEF/UNREF) is particularly suitable for situations where fine-tuning is required, such as adjusting screws.