The working principle of a nut is self-locking through the friction between the nut and the bolt. However, the reliability of this self-locking decreases under dynamic loads. In some critical situations, we take anti-loosening measures to ensure the reliability of the nut's tightening. Using a lock nut is one such anti-loosening measure.
There are three types of lock nuts:
The first type uses two identical nuts screwed onto the same bolt, applying a tightening torque between the two nuts to ensure a reliable bolt connection.
The second type is a dedicated anti-loosening nut, which needs to be used with an anti-loosening washer. This dedicated anti-loosening nut is not a hexagonal nut, but a round nut with 3, 4, 6, or 8 notches on its circumference (depending on the nut size and the manufacturer's product series). These notches serve as both the application points for the tightening tool and the entry points for the anti-loosening washer.
The third type has through-holes (usually two, spaced at 90 degrees on the outer surface) drilled from the outer surface of the nut to the inner threaded surface. These holes are used to screw in small-diameter countersunk screws, applying a centripetal force to the threads to prevent the lock nut from loosening. Higher-quality lock nuts sold on the market have small copper pieces on their inner surface that match the nut's thread. This prevents the radial tightening screw from directly contacting and damaging the locked threads. This type of lock nut is increasingly used in locking the shaft ends of rotating parts, such as preventing loosening of bearings on the mounting end of ball screws.