Mil spec MIL-DTL-18240 (supersedes MIL-F-18240) defines the requirements for self-locking elements for use in externally threaded fasteners such as bolts and screws to be used in fasteners with either UNC, UNJC, UNF, UNJF, UNRC or UNRF threads and where the temperatures will not exceed 250°F.
- Type N – Plug/pellet
- Type L – Strip
- Type P – Patch