Coarse teeth:
It is not necessary to mark the pitch, such as M8, M12-6H, M16-7h, etc., mainly used as the coupling thread. Compared with the fine thread, the pitch is large, the angle of the thread is also large, the self-locking property is poor, and the spring washer is generally used. Used together: the pitch is large, the tooth shape is also deep, and the strength of the body member is also reduced. The advantage is that it is easy to disassemble and assemble, and the standard parts are complete and easy to interchange.Fine teeth:
The pitch must be marked to show the difference from the coarse thread. The characteristics are the opposite of the coarse teeth. It is specified to supplement the special requirements for the coarse thread. The fine thread also has a pitch series, which is mainly used in the hydraulic system. Pipe fittings, mechanical transmission parts, thin-walled parts with insufficient strength, space-constrained internal parts and shafts with high self-locking requirements.
To determine whether the thread is coarse or fine, first determine the purpose of the thread. Use the caliper to measure the length of the n pitches. After dividing by n, check the thread table.
The thick strength is high and the sealing is fine. The same level guarantees that the load is not much different (slightly higher teeth), and the tightening load of the two is close when used for fastening. The anti-loosening effect of fine thread is better than that of coarse teeth when no anti-loose measures are taken. It is generally used for thin-walled parts and parts with high requirements for anti-vibration.
Fine threading has advantages when used for adjustment. Disadvantages of fine thread: It is not suitable for application on materials with excessive coarseness and poor strength. When the tightening force is too large, it is easy to slide.
Fine thread and coarse threaded screws are used for fastening purposes . Fine screws are generally used to lock thin-walled parts and parts with high requirements for anti-vibration. Fine thread has good self-locking performance, so it has strong anti-vibration and anti-loose ability. However, due to the shallow depth of thread, the ability to withstand greater tension is worse than that of coarse thread. The strength of the fine thread is lower than that of the standard thread (coarse). The standard thread actually adopts the principle of equal strength, that is, the strength of the thickness of the standard nut, which is equivalent to the strength of the screw, from the perspective of strength. This design is the most reasonable.
So standard threads are the most widely used. However, it also has the disadvantage that the self-locking is relatively inferior to the fine thread, so a spring washer or other self-locking device should be added in the place where the vibration is severe. Fine thread is generally not used for large stress work, it is mainly used for positioning, adjustment, fixing and so on. It is characterized by the fact that the outer diameter of the nut can be much smaller than the standard thread, and is particularly suitable for thin-walled cylindrical parts, such as fine threading, which is widely used in various optical instruments. In addition, the self-locking property of the single-head fine thread is very good, and it can be used for precise adjustment and control, and many of them are used in a micrometer-like measuring instrument. The disadvantage of fine thread is that the thread is easily damaged, affecting the installation and disassembly. A slight dimensional error may cause the screw to be damaged at the same time.
1. Application of coarse thread Thread The coarse thread series (M/UNC/UNRC) is generally used for the mass production of threaded fasteners, such as bolts, screws and nuts. It has unique advantages in requiring quick assembly or disassembly and some barbaric operations that are prone to rust and damage. However, its self-locking properties are not as good as fine teeth and ultra-fine thread.
2, fine thread application applications Fine thread series (MF / UNF / UNRF) is usually used in applications requiring high fastener strength. Since the fine thread is shallower than the coarse thread and the thread has a small diameter, the thread strength is higher than that of the coarse thread of the same specification. In addition, fine thread can be used for fine tuning applications.
3. Ultra-fine thread thread application The ultra-fine thread series (UNEF/UNREF) is especially suitable for occasions where fine adjustment is required, such as adjusting screws.
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