Locknuts are a type of prevailing-torque fastener that resists loosening under vibration and torque. They differ from standard nuts because they typically have friction-increasing bearing surfaces (e.g., pitted grooves on flanges) or special internal thread-geometries. In addition to locknut type, these fasteners carry thread specifications and differ in terms of materials of construction, product features, and approvals. Locknuts are available in inch-based and metric designations, and have a numeric (e.g., # 1) or alphanumeric (e.g., M.2) description.
Castle nuts are locknuts that have slots or notches that are cut into one end to allow a cotter pin or safety wire to assist in fastening. Castle nuts resemble a chess-playing piece and are also known as castellated or slotted locknuts. Distorted-thread locknuts use a deformed section of thread to prevent loosening due to vibration from or rotation of the clamped item. Categories include center-lock, elliptical-offset, top-lock, oval, and non-slotted hex. Flex-top locknuts or split-beam locknuts are made from a single piece of material and have a slotted top that expands as the nuts are tightened. This locks them into place and provides vibration resistance.
Interfering threadnuts or tapered thread nuts are a type of locknut that has an over-sized root diameter to provide permanent or semi-permanent joining. Jam nuts are typically half the height of a standard nut. Often, these locknuts are pushed-up or jammed against a standard nut in a fastener assembly to provide an additional securing force. Jet nuts or K-nuts are smaller, flanged-type locknuts that are often used in aerospace or automotive racing applications. Speed nuts (sheetmetal nuts, tinnerman nuts) can be quickly pushed into place using deformable teeth instead of standard threads. Two-piece locknuts are sold as two-component, upper and lower nut assembly pairs.
Locknuts are available with right-hand (clockwise) or left-hand (counterclockwise) threads. Some are made of metal materials such as aluminum, brass, bronze, copper, steel, or titanium. They may be anodized, galvanized, nickel-plated, zinc-plated, or treated with other finishes. Non-metallic locknuts made of plastic, rubber, and nylon are also available. Locknuts that are sold as an assembly have a non-integral or secondary-material hardware, typically a washer or plastic insert, to improve their mechanical performance.
