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Nylon lock nuts ('Nyloc')

A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,[1] stiff nut[1] or elastic stop nut,[2] is a nut that resists loosening under vibrations and torque. Elastic stop nuts and prevailing torque nuts are of the particular type where some portion of the nut deforms elastically to provide a locking action.[2] The first type used fiber instead of nylon and was invented in 1931.[3]

Locknuts, jam nuts, lock washers, and thread-locking fluid are ways to prevent vibration from loosening a bolted joint.


There are various kinds of specialised lock nuts, including:

Prevailing torque values[edit]

Prevailing torque[6] differentiates a locknut from a free spinning nut based on a value of how much torque is required during installation before clamp loading. For example, on a nylon-insert nut, it is the torque needed to overcome the resistance of the nylon dragging across the mating thread. This torque value is usually not very high relative to final installation torque. Tolerance ranges for torque are specified in some standards such as (ISO, DIN, IFI, ASME, SAE, AN-, MS-, NAS- NASM-).

See also[edit]



  1. ^ a b Glossary of Terminology Related to Nuts and Bolts, retrieved 2008-11-30.
  2. ^ a b Smith 1990, p. 104.
  3. ^ "Nut With Elastic Ring Can't Work Loose", April 1931, Popular Science bottom of page 67 drawing of how lock nuts work
  4. ^ K-NUTS.com, retrieved 2012-03-01.
  5. ^ fastenerdata.co.uk, retrieved 2019-03-08.
  6. ^ Kaindl, Mike. "The Locknut Whisperer". blogspot. Retrieved 3 June 2014.


External links[edit]