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2-Way Reversible Lock Nuts

An inexpensive, one piece all-metal prevailing torque type hex lock nut with two or three equally spaced round or rectangular indentations compressed onto the flat sides of the nut. These compressions create distort the internal threading and results in an increased resistance when tightened onto mating threads. Two-way reversible lock nuts are considered "two way" because they can be installed in either orientation (top up, top down). These nuts are also referred to as centerlock nuts, and are ideal for production and automated assembly. Since the locking mechanism occurs in the center of the nut, screw length can be reduced, because threads need not protrude from the nut to lock securely. All-metal lock nuts are more resistant to higher temperatures and chemical exposure than non-metallic lock nuts (such as nylon insert lock nuts).


The distortion in the threading of the nut produces friction between threads of mated components resulting in increased resistance to loosening forces. Consequently, unlike free spinning lock nuts, torque must be applied during both assembly and dis-assembly - prevailing torque. The advantage of this type of nut is that loosening is unlikely even if pre-load is reduced completely because of the remaining rotational resistance. Prevailing torque lock nuts are not ideal to use with long threaded assemblies because long spans of threads may reduce the effectiveness of the nut's locking mechanism. Therefore, the length of the bolt or screw should not be much longer than that needed to ensure full thread engagement with the nut.

Material, Threading and Sizes

Available threads include standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine). Sizes refers to the nut's nominal thread diameter. Nut width across flats, (wrench size), and thickness vary with nut size.

Typically, sizes range from about #4 to 1". Sizes less than 1/4" are listed as a number size (the larger the number the larger the size) while sizes that are 1/4" and larger are specified in inches, usually fractional rather than decimal. Two-way reversible Lock nuts are available in a low-carbon steel which conforms to the following chemical composition requirements- Carbon: 0.47%max.; Phosphorus: 0.12% max.; Sulfur: 0.23% max. For dimensions and technical specifications click here.