How is the locking feature of the fiber-type locknut obtained?

• A. By thread friction
• B. By a metal insert
• C. By the use of an unthreaded fiber locating insert
• D. By a spring clip

Answer: (C)

Fiber-type locknuts rely on a piece of fiber inside the nut that is not threaded. When the nut is tightened onto a bolt, the bolt threads bite into this unthreaded fiber and deform it, creating a friction-based lock that resists loosening under vibration. That fiber insert acts as a compliant, interposed barrier between the nut and bolt threads, producing the locking action. So the best description is using an unthreaded fiber locating insert inside the nut. The other methods—relying on plain thread friction, a metal insert, or a spring clip—don’t provide the specific fiber-based locking mechanism used in these nuts.