This is the most widely used anti-loosening method. This method generates a positive pressure between the thread pairs that does not follow the external force, so as to generate a friction force that can restrain the relative rotation of the thread pairs. This positive pressure can be achieved by pressing the thread pair axially or simultaneously in two directions. For example, elastic washers, double nuts, self-locking nuts and nylon insert lock nuts are adopted. This kind of anti-loosening method is more convenient for disassembly of the nut, but in the environment of impact, vibration and variable load, the pre-tightening force of the bolt will be reduced due to slack at the beginning. As the number of vibrations increases, the lost pre-tightening force is dull. The increase will eventually lead to the loosening of the nut and the failure of the threaded connection.