Which nut design is intended to resist loosening under vibration by incorporating a locking feature?

• A. Hex Nut
• B. Lock Nut
• C. Wing Nut
• D. Cap Nut

Answer: (B)

When a fastener is subjected to vibration, it can loosen because the applied forces try to rotate the nut and reduce the clamping force. A lock nut includes an integral locking feature that increases friction or mechanically binds the threads, so the nut resists rotation and stays tight as loads fluctuate. This locking action can come from a nylon insert, deformed threads, or other locking mechanisms built into the nut, allowing it to hold its preload under vibration.

The other nuts don’t include such a locking mechanism: a standard hex nut provides only basic clamping with no built-in lock; a wing nut is designed for easy hand tightening, not locking under vibration; a cap nut is mainly for covering the threads and protection, with no locking function.