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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. Prevailing torque nuts have some portion of the nut that deforms elastically to provide a locking action.[2] Free-spinning locknuts exist which carry the advantage of not requiring extra torque until seated.[3]


There are various kinds of specialised lock nuts, including:

Prevailing torque values[edit]

Prevailing torque[7] 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-).

Prevention of loosening[edit]

Locknuts are one way to prevent vibration from loosening a bolted joint. Other methods include safety wire, lock washers, and thread-locking fluid.

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. ^ "StackPath". www.machinedesign.com. Retrieved 2022-03-31.
  4. ^ K-NUTS.com, retrieved 2012-03-01.
  5. ^ fastenerdata.co.uk, retrieved 2019-03-08.
  6. ^ Gong, Hao; Liu, Jianhua; Feng, Huihua (2022-02-01). "Review on anti-loosening methods for threaded fasteners". Chinese Journal of Aeronautics. 35 (2): 47–61. doi:10.1016/j.cja.2020.12.038. ISSN 1000-9361. S2CID 234300791.
  7. ^ Kaindl, Mike. "The Locknut Whisperer". blogspot. Retrieved 3 June 2014.


External links[edit]