AYA FASTENERS Guide | Coarse Thread And Fine Thread Fasteners, How To Choose?

Coarse threads can be defined as standard threads, while fine threads are relatively coarse threads. Under the same nominal diameter, the number of teeth per inch is different, that is, the pitch is different. The coarse pitch is large, while the fine pitch is small. In other words, for the two specifications of 1/2-13 and 1/2-20, the former has coarse teeth and the latter has fine teeth. Therefore expressed as 1/2-13UNC and 1/2-20UNF.

Since there are two different thread specifications with the same nominal diameter, how do we choose between coarse thread and fine thread?

coarse thread

The so-called coarse thread actually refers to standard thread. Unless otherwise specified, the threaded fasteners we generally buy are coarse thread.

Coarse threads are characterized by high strength, good interchangeability, and there are standards for comparison. Generally speaking, coarse threads should be the best choice. Compared with fine threads, due to the large pitch and large thread rise angle, the self-locking properties are 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, and the supporting standard parts are complete and easy to interchange.

There is no need to mark the pitch when marking coarse threads, such as M8, M12-6H, M16-7H, etc., which are mainly used for connecting threads.

fine thread

Fine threads and coarse threads are just the opposite and are specified to supplement special use requirements that coarse threads cannot meet. Fine threads also have a pitch series. The pitch of fine threads is smaller, so it is more conducive to self-locking and anti-loosening and has more teeth, which can reduce leakage and achieve a sealing effect. In some precision situations, fine-thread screws are more convenient for precise control and adjustment.

The disadvantage is that the tensile value and strength are lower than those of coarse threads, and the threads are easily damaged. It is not recommended to disassemble and assemble multiple times. The matching nuts and other fasteners must also be equally accurate, otherwise, the dimensional error will easily cause damage to the screws and nuts.

When marking fine threads, the pitch must be marked to show the difference from coarse threads.

Coarse thread and fine thread fasteners, how to choose?

Both coarse thread and fine thread bolts are used for fastening. However, fine-thread bolts are generally used to lock thin-walled parts and parts with relatively high anti-vibration requirements. Fine threads have good self-locking properties, so they have strong resistance to vibration and loosening. However, due to the shallow depth of the threads, their ability to withstand greater pulling force is worse than that of coarse threads. When no anti-loosening measures are taken, the anti-loosening effect of fine threads is better than that of coarse threads.

When used for adjustment, fine threads have more advantages. But it also has certain disadvantages: it is not suitable for use on materials with excessively thick structures and poor strength. When the tightening force is too large, it is easy to slip.

The thread thickness should be selected according to the specific usage scenario. If you have any questions about fastener selection, please feel free to contact AYA Fasteners.

Looking for Fasteners?
Click below to browse AYA FASTENERS' extensive Fastener catalog, including high-quality screws, bolts, nuts, and washers products.

CONTACT AYA FASTENERS