Self-locking nuts use either a pre-installed plastic insert or a chemical substance applied to the threads that, when initially tightened down, spreads in between the threads to create a more stable adhesive bond than the metal-to-metal connection of an ordinary nut and bolt. Locking nuts keep a threaded nut and bolt assembly from coming loose due to vibration and loss of torque required to maintain structural integrity.
Self-locking nuts and bolts can be purchased with factory-installed locking components. These components are engineered plastics, such as metal wedge pieces used for extra heavy-duty applications, or poly chemical applications already on the threads. In addition to pre-prepared nuts and bolts, do-it-yourself chemical products are available to manually apply to the threads.
Both types of products provide the same results in keeping the nut secured to the bolt despite vibration, plus they inhibit rust and leaks. Nuts with the pre-applied factory inserts or chemicals provide the added advantage of speed, being ready to use without preparation, while the self-applied chemicals take time to apply to each nut or bolt and may require dry time. In addition, depending on the material the nuts are made from, the application of a primer may be necessary.