As shown in Figure 1, there is a 30 ° wedge-shaped inclined surface at the bottom of the female thread. When the bolt and nut are tightened to each other, the tip of the bolt is firmly pressed against the wedge-shaped surface of the self-locking thread, thereby generating a large locking force. . Due to the change of the angle of the tooth shape, the normal force generated by the contact between the threads forms an angle of 60 ° with the bolt axis, instead of forming an angle of 30 ° as with ordinary threads. Obviously, the normal pressure of the thread is much larger than the tightening pressure, so the anti-loosing friction force will inevitably increase greatly.

When the bolt tension is also P0, the normal pressure of the traditional 60 ° angle thread P = 1.15P0,

Since the self-locking thread has a wedge-shaped bevel at a 30 ° angle,

The angle and the magnitude of the normal pressure have changed. The normal pressure P = 2P0. The ratio of the normal pressure of the two is about 12: 7. The anti-loosing friction of the self-locking thread has increased accordingly.

The wedge-shaped surface of the self-locking thread can also remove problems such as uneven force on the ordinary thread and tripping and biting.

Ordinary thread—The 60 ° angle V-shaped thread carries a load of 70% to 80% on the first thread engaging surface and the second thread engaging surface, while the subsequent several engaging surfaces bear little load. In this way, under the condition of working vibration load of ordinary threaded fasteners, it is easy to overcome the locking force on the thread contact surface to cause rotation, and then loosen.

This is why ordinary threaded fasteners come loose.