ASME B18.16.6 is the governing American national standard for prevailing torque type steel hex nuts with a non-metallic (typically nylon) insert. This standard defines the dimensional and performance requirements for lock nuts designed to resist loosening under extreme vibration and dynamic loading in inch-series assemblies.

The nylon insert creates a frictional interference fit with the mating bolt threads, providing a constant "prevailing torque" that maintains joint integrity even if the initial axial tension is partially lost. It is a cornerstone of North American automotive and industrial safety fastening.

The ASME B18.16.6 lock nut utilizes a captured polymer ring within a recessed cavity at the top of the nut. As the bolt enters the nylon insert, the polymer deforms elastically over the bolt threads, creating a high-friction radial compressive force. This design allows for multiple reuses (within limits) and provides a non-marring locking action that does not damage the mating bolt's thread coating.

• Automotive suspension and engine vibration management
• North American heavy trucking and trailer assemblies
• Agricultural equipment and harsh-environment machinery
• Renewable energy (Wind turbine nacelle assembly)