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.

　　第二種方式是機械防松。是用止動件直接限制螺紋副的相對轉動。如采用開口銷、串連鋼絲和止動墊圈等。由于止動件沒有預緊力，螺母松退到止動位置時防松止動件才能起作用，因此，這種方式實際上不防松而是防落。

　　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.

　　第三種方式是鉚沖防松。在擰緊后采用沖點、焊接、粘接等方法，使螺紋副失去運動副特性而連接成為不可拆連接。這種方式的缺點是栓桿只能使用一次，且拆卸十分困難，必須破壞螺栓副方可拆卸。

　　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.

　　第四種方式是結構防松。是利用螺紋副自身結構，即唐氏螺紋防松方式。

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