Lock nut

Other names: root nut, lock nut and nut.
Purpose: lock the threaded external connector or other pipe fittings.
The working principle of nut is self-locking by friction between nut and bolt. However, the reliability of this self-locking will be reduced under dynamic load. On some important occasions, we will take some anti-loosening measures to ensure the reliability of nut locking. Lock nut is one of the anti-loosening measures.
There are also three types of lock nuts:
The first is to screw two identical nuts on the same bolt, and add a tightening torque between the two nuts to make the bolt connection reliable.
The second is a special lock nut, which needs to be used with a lockable gasket. The special lock nut is not a hexagon nut, but a middle round nut. There are 3, 4, 6 or 8 notches on the circumference of the nut (depending on the size of the nut and the product series of the manufacturer). These notches are not only the focus of the tightening tool, but also the clamping point of the lock pad bayonet.
The third is to drill through threaded holes from the outer circle surface of the nut to the inner circle thread surface (generally 2, 90 distributed on the outer circle surface), which are used to screw in small diameter countersunk screws. The purpose is to exert a centripetal force on the thread to prevent the lock nut from loosening. The lock nut with good quality sold on the market is inlaid with a small copper block with the same thread as the lock nut on the inner circle of the nut to prevent the radial jacking screw from directly contacting the locked thread and damaging the latter. This kind of lock nut is gradually applied to the shaft end locking of rotating parts, such as the anti-loosening of the bearing at the mounting end of the ball screw.
The second anti-loosening method is more reliable than the first, but the structure is relatively complex. Compared with the first two, the third clock has the characteristics of better anti-loosening effect, simpler and more beautiful structure and smaller axial size.