How to distinguish the coarse thread and fine thread of screws and nuts, what are the advantages and

2023-03-14 14:29

We all know that screws and nuts have coarse teeth and fine teeth, so the screw and nut must be detailed to what level, can be called fine thread? From the industry application, coarse thread is generally reference thread; And fine thread is quite coarse teeth, in the same outside diameter, the number of teeth per foot contains is not the same, in fact, the pitch is not the same, coarse tooth pitch is large, and fine tooth pitch is small. In other words, for the 1/2-13 and 1/2-20 models, the first one is thick and the second one is fine. So it's 1/2-13UNC and 1/2-20UNF.

Even if there are two different sizes of thread in the same outside diameter, how can coarse and fine thread be used?

Coarse thread for screws and nuts

The screw nut rough teeth actually refers to the standard thread, in the absence of special instructions, we generally choose screws and other standard parts are rough teeth. Coarse thread is characterized by high compressive strength, good exchangeability, and specifications can be compared, generally speaking, screws and nuts coarse teeth should be a better choice; Compared with fine thread, because of the large pitch, thread Angle is also very large, self-locking is only poor, in the vibration environment need to be modified anti-loose sealing ring, self-locking device; It is characterized by convenient disassembly, complete with supporting standard parts, very easy to exchange; It is not necessary to indicate the pitch when the coarse thread is marked, such as M8, M12-6H, M16-7H, etc., specially for the application of connecting thread.

Fine thread

Screw and nut fine teeth and coarse teeth on the contrary, is to fill the coarse tooth thread can not meet the unique use requirements of the provisions, fine tooth thread is also a series of products with pitch, fine tooth pitch is relatively small, so it is more beneficial to self-locking, anti-loose, and the number of teeth more and more, can reduce the leakage effect, achieve the actual effect of sealing. In some high precision places, fine tooth screws are more convenient for accurate control and adjustment.

The main screw and nut should be weak compressive strength value, compressive strength is low, and thread is very easy to damage, it is not recommended to disassemble several times, and its supporting nuts and other standard parts may be the same exact, specifications slightly deviated, it is very easy to promote screw nuts at the same time damage. Mainly used in hydraulic system pipe, mechanical equipment transmission equipment, screw nut compressive strength is not enough thin wall parts, limited by space fuselage parts and self-locking requirements of high shaft. When fine thread is indicated, the pitch should be indicated to show the difference between coarse thread and fine thread.

How to use coarse and fine thread

Coarse thread and fine thread screws of screws and nuts are also used for tightening in the application field. Fine thread screws are generally used for locking thick-walled parts and parts with high shock resistance requirements. The self-locking of fine thread is cost-effective, so the ability to resist vibration and loose is very strong, but because of the deep shallow thread teeth, bear more tension resistance than coarse thread. When screws and nuts do not use anti-loosening countermeasures, the anti-loosening performance of fine thread is better than that of coarse teeth. It is generally used for thick-walled parts and parts with high requirements for shock resistance. Making adjustments takes time, and fine thread has an advantage. Defects of fine thread: it is not suitable for use on materials with too strong and poor compressive strength. When the twisting force is a little larger, it is very easy to slip buckle.

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