Machine Design

Prevailing-Torque Locknuts

A built-in locking feature develops full locking action as soon as these nuts are engaged with the bolt threads. They must then be wrenched to final seated position.

Several of the locking techniques rely on a distortion of the nut thread or shape to create an interference fit. Metal or nonmetal inserts (plugs, strips, or collars) that plastically deform are also used to create an interference fit. Sometimes, separate locking pins, wires, or springs are fitted to the nut, or the nut may have a large slotted crown with springlike fingers that grip the bolt.

Ideally, prevailing-torque nuts should be used with the minimum thread engagement necessary to develop the holding strength of the nut and the locking action. Torquing these nuts over a long thread travel under load could damage the locking feature.

Prevailing-torque locknuts can also be used as spacer or stop nuts where components must be free to rotate without end play.

TAGS: Fasteners
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