The first is friction and anti loosening. This is the most widely used anti loosening method, which produces a positive pressure between the thread pairs that does not change with the external force to produce a friction force that can prevent the relative rotation of the thread pairs. The positive pressure can be achieved by pressing the thread pair axially or simultaneously. For example, elastic washer, steel connecting sleeve, self-locking nut and nylon insert lock nut are used. This anti loosening method is convenient for nut disassembly, but in the case of impact, vibration and variable load, the pre tightening force of the bolt will decrease at the beginning due to relaxation. With the increase of vibration times, the lost pre tightening force will slowly increase, which will eventually lead to nut loosening and thread coupling failure.

　　第二种方式是机械防松。是用止动件直接限制螺纹副的相对转动。如采用开口销、串连钢丝和止动垫圈等。由于止动件没有预紧力，螺母松退到止动位置时防松止动件才能起作用，因此，这种方式实际上不防松而是防落。

　　The second is mechanical locking. It is to directly limit the relative rotation of the thread pair with the stopper. Such as the use of cotter pin, steel wire and stop washer. Since the stop has no pre tightening force, the stop can only work when the nut is loosened and retreated to the stop position. Therefore, this method does not prevent loosening but falling off.

　　第三种方式是铆冲防松。在拧紧后采用冲点、焊接、粘接等方法，使螺纹副失去运动副特性而连接成为不可拆连接。这种方式的缺点是栓杆只能使用一次，且拆卸十分困难，必须破坏螺栓副方可拆卸。

　　The third way is riveting and punching. After tightening, punching, welding, bonding and other methods are used to make the thread pair lose the characteristics of the moving pair and become a non detachable connection. The disadvantage of this method is that the bolt rod can only be used once, and it is very difficult to disassemble, so the bolt pair must be destroyed before disassembly.

　　第四种方式是结构防松。是利用螺纹副自身结构，即唐氏螺纹防松方式。

　　The fourth way is to prevent the structure from loosing. It uses the thread pair's own structure, i.e. down thread locking mode.