A nyloc nut, also known nylon insert lock nut, polymer insert lock nut or elastic stop nut (although incorrectly, as an elastic stop nut is broad class of locking nuts), is a kind of nut

Nut (hardware)

A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

 that includes a nylon

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

 collar insert. The insert is placed at the end of the nut and its inner diameter (ID) is slightly smaller than the major diameter of the screw. The insert deforms elastically over the threads of the screw, but threads are not cut into the nylon. The nylon insert locks the nut in two ways. First, it forces the bottom face of the screw threads against the top face of the nut threads, increasing the friction

Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

 between the two. Second, the nylon applies a compressive force against the screw itself. Nyloc nuts retain their locking ability up to 250 °F (121.1 °C).

Nyloc is a registered trade name

Trade name

A trade name, also known as a trading name or a business name, is the name which a business trades under for commercial purposes, although its registered, legal name, used for contracts and other formal situations, may be another....

 of Forest Fasteners. In Australia "Nyloc" is a registered trade mark of Exafast Pty Ltd.

Nylon pellet nut

A nylon pellet nut is very similar to a nyloc nut except that it uses one or more smaller nylon inserts instead of a ring of nylon. They do not lock as strongly as nyloc nuts.

Reuse

Authorities disagree on whether nyloc nuts should be reused. For example, Smith notes that the nylon insert is not damaged by installation and therefore they can be reused many times, and a Federal Aviation Administration

Federal Aviation Administration

The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 Advisory Circular allows nuts to be reused if the prevailing torque is within specification. However, an Air Force

United States Air Force

The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

Technical Order requires replacement of self-locking nuts in critical areas. Various specifications for aerospace-grade self-locking nuts require that the running torque be maintained after a number of cycles of assembly, but without preloading the fastener.