Locknuts, also known as a prevailing torque nuts, stiff nuts, or elastic stop nuts resist loosening caused by machine vibrations and torque. They are commonly used by machinists, engineers, and mechanics, and there are two general types of locknuts: prevailing torque and surface-bearing.

Prevailing Torque

Designed with a built-in locking feature that functions when it’s engaged with the bolt threads and then must be tightened with a wrench. Several of the locking techniques rely on distorted threads or a distorted shape to create an interference fit. Metal or nylon inserts can also be inserted to create the interference fit. A few common types of prevailing torque lock nuts include: 2-way reversible, flex-type, stover, all metal, and nylon insert.


These are free spinning nuts that require tightening against a bearing surface in order for the locking mechanism to work. This type is not recommended for use on fragile parts. A few common types of free spinning lock nuts include: serrated flange, spring head, and KEPS (K-Lock)

Locknuts from AFT Fasteners are available in a wide range of diameters and materials including alloy steel, carbon steel and stainless steel with cadmium, phosphate and zinc finishes. Search our standard and metric locknuts, or contact us today for assistance finding the specific part you need. Our knowledgeable staff is here to help.