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Glossary
Prevailing Torque Nut
A prevailing torque nut is a locknut with a built-in feature that creates friction on the threads, producing a constant “drag” (the prevailing torque) as it turns. That friction resists loosening from vibration or shock, even when clamp load is low, making the joint more reliable than with a standard nut alone.
There are two main styles: nylon-insert (Nylock), which uses a polymer ring to grip the bolt and is best for general use but limited to about 120 °C/250 °F and a few reuses; and all-metal (distorted-thread/top-lock), which relies on deformed metal threads to pinch the bolt, tolerating higher temperatures and harsher service with limited reusability (the locking torque drops with cycles). Installation torque specs typically account for the added drag, and performance can vary with plating, lubrication, temperature, and reuse. These nuts are common in automotive, machinery, and structural applications where vibration resistance is critical.
