Definition
A specialized nut with notches, slots, or holes around its outer edge that is tightened or loosened with a matching spanner wrench rather than a standard open-end or socket wrench. Spanner nuts are commonly used to retain bearings, seals, and rotating components on shafts where a low-profile, evenly torqued fastener is required.
Plain English
A round nut with notches cut into it. You can't turn it with a normal wrench -- it needs a special tool that fits into the notches.
Context Anchor
Seen in aircraft maintenance on parts that need a secure fit or careful adjustment, such as bearing retainers, landing gear parts, or other assemblies specified by the maintenance manual.
Derivation
Spanner' is the British term for a wrench, originally referring to a tool that 'spanned' the distance across a fastener. A spanner nut is simply a nut designed to be turned by a spanner-style tool that engages its notches.
Why Pilots Care
Proper torque on these nuts keeps propellers and rotating assemblies securely attached during flight.
Intuition Check
Do not read spanner nut as the wrench itself. The spanner nut is the nut; the spanner wrench is the tool that turns it.
Example Sentence 1
The mechanic used a spanner wrench to back off the spanner nut securing the wheel bearing.
Example Sentence 2
After the engine run, the technician rechecked the spanner nut for any movement.