Rick's Free Auto Repair Advice

Prevailing torque nut

What is a prevailing torque nut?

A prevailing torque nut looks like an ordinary nut that has been squashed slightly so the threads are in an oval shaped pattern.

prevailing torque nut

Prevailing torque nut used on axle shafts. Notice the deformed threads and the slightly oval shape.

The prevailing torque nut nut will start on the bolt or shaft threads easily until it reaches the deformed threads. As you continue to apply torque to the nut, you gradually form the oval threads into a circle to match the bolt or shaft. The deformation force is what prevents the nut from loosening.

A prevailing torque nut is a one-time use item. Once it has been forced into a circle, it cannot be reused because it has lost its ability to retain torque. If you reuse a prevailing torque nut, it will loosen by itself.

Where prevailing torque nuts are used

These oval shaped nuts are commonly used on axle shafts, ball joints, strut mounting bolts and steering components. They reduce manufacturer installation cost because they eliminate the need for castle nuts and cotter keys and thread locking sealants.

©, 2017 Rick Muscoplat

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