Definition
A self-locking nut designed to resist loosening from vibration. The locking action is produced by a fiber or nylon insert, or by a deformed metal section, that grips the bolt threads and prevents the nut from backing off on its own.
Plain English
A nut that won't shake loose. Once tightened, it stays put because something inside it grips the threads of the bolt.
Context Anchor
Seen in aircraft maintenance, parts lists, and inspections wherever hardware must stay secure despite vibration.
Derivation
Called a stop nut because it stops itself from turning -- the insert or deformed thread halts rotation once the nut is in place.
Why Pilots Care
Vibration in flight can loosen ordinary nuts, leading to loss of critical fasteners and potential structural or control failure.
Intuition Check
A stop nut is not a nut used to stop a moving part. The “stop” idea here means it helps stop the nut itself from backing off the threads.
Example Sentence 1
The mechanic replaced the stop nut on the elevator control rod because fiber-insert nuts lose their locking ability after being removed and reinstalled.
Example Sentence 2
During the 100-hour inspection, all stop nuts on the control surface hinges were checked for proper torque and locking action.