The working principle of the semi-circular nut is to achieve self-locking through the friction between the nut and the bolt. However, in dynamic loads, the reliability of this self-locking decreases. In critical applications, we take certain anti-loosening measures to ensure the reliability of the semi-circular nut's tightness. One such measure is the locking nut. The effectiveness of the anti-loosening effect of the locking nut primarily depends on the interaction force between the mating threads of the nut and the bolt. Currently, there are many ways to increase the interaction force between the mating threads, such as the anti-loosening nut with improved thread structure from the SAE nut, which requires the use of an anti-loosening washer. The anti-loosening nut is not a hex nut but a semi-circular nut, with 3, 4, 6, or 8 notches around the circumference (varies depending on the nut size and manufacturer's product series). These notches serve as both the points of force for the tightening tool and the insertion points for the anti-loosening washer.