Nylock

Nylock is a trademarked name used for a type of prevailing torque fastener, commonly referred to as a nylon lock nut. The device consists of a standard hex or wing nut with a small insert of nylon polymer placed in the threads. When the nut is torqued onto a bolt, the nylon deforms slightly and exerts a frictional force against the mating threads, providing resistance to loosening caused by vibration, shock, or thermal cycling. The nylon insert typically occupies only a portion of the thread length, allowing the nut to be reused a limited number of times before the polymer degrades.

The concept originated in the mid‑20th century as manufacturers sought a simple, cost‑effective alternative to prevailing‑torque washers and split‑lock nuts. Over time, variations have been developed, including all‑metal lock nuts with a prevailing torque feature, and hybrid designs that combine nylon inserts with other locking mechanisms such as jammed or distorted threads. Nylon lock nuts are produced in a range of sizes and materials, most commonly stainless steel, carbon steel, and brass, to suit different corrosion‑resistance and strength requirements.

Common applications include automotive engine assemblies, machinery, aerospace components, and consumer electronics where fasteners are subject to repeated vibration. Advantages of Nylock nuts include ease of installation, low profile, and inexpensive manufacturing. Limitations involve reduced reusability—typically three to four installs—because the nylon loses its elastic properties, and decreased performance at elevated temperatures where the polymer may soften. Standards such as ISO 15058 and ASTM A563 define the dimensional and performance criteria for these fasteners.