Definition
A hand tool used to tighten or loosen round nuts that have notches or slots cut into their outer edge. The tool has a curved arm with a hook or pin on the end that fits into one of the notches, allowing the technician to apply turning force to the nut.
Plain English
A specially shaped wrench with a hook on the end. The hook catches into a slot on the edge of a round nut so you can turn it. Regular wrenches won't grip these nuts because they have no flat sides.
Context Anchor
Seen in aircraft maintenance instructions when a round locking nut, bearing collar, or adjustable ring must be loosened or tightened without damaging it.
Derivation
From 'hook' (the curved catching end of the tool) and 'spanner' (the British term for a wrench, from the German 'spannen,' meaning to tighten or stretch). The name simply describes what it is: a wrench with a hook.
Why Pilots Care
Pilots themselves rarely use a hook spanner, but understanding the term helps when reviewing maintenance records or discussing repairs with a mechanic.
Intuition Check
Do not think of a hook spanner as a general-purpose wrench. It is made to grip a notch or slot in a round part.
Example Sentence 1
The mechanic used a hook spanner to remove the bearing retainer nut on the propeller shaft.
Example Sentence 2
Using the correct hook spanner prevents damage to the slots on the locknut during torquing.