A jam nut, also known as a half-height nut, is a specialized fastener that stands at approximately 50% the height of a conventional nut. This compact design serves two primary purposes.

First, it functions as an effective locknut by being tightened or "jammed" against a regular nut, creating a secure mechanical lock that prevents loosening due to vibration or movement.

Second, its slim profile makes it invaluable in confined spaces or tight clearance applications where standard-height nuts would be too tall to fit properly. This versatility makes jam nuts essential in various mechanical assemblies.