Definition
A threaded nut designed to resist loosening from vibration without the need for a separate locking device such as a cotter pin or safety wire. The locking action is built into the nut itself, typically through a deformed metal collar, a fiber or nylon insert, or distorted threads that grip the bolt firmly when tightened.
Plain English
A nut that holds itself tight on a bolt and won't shake loose, even when the aircraft vibrates. It does this on its own — no extra pin, wire, or washer needed to keep it in place.
Context Anchor
Seen in aircraft maintenance, inspection notes, and parts descriptions for hardware used on engines, airframes, and control-system attachments.
Derivation
Combines 'self' (by its own means) with 'locking nut' to indicate the fastener secures itself against loosening.
Why Pilots Care
Prevents critical fasteners from vibrating loose in flight, avoiding component failure or loss of control.
Intuition Check
Self-locking does not mean permanent or maintenance-free. It means the nut has its own added grip, but it must still be installed correctly and replaced if it no longer holds tightly.
Example Sentence 1
The mechanic replaced the self-locking nut on the control rod because the nylon insert had hardened and no longer gripped the bolt threads.
Example Sentence 2
Self-locking nuts are used on the landing gear bolts because of constant vibration.