Definition
A small, round, tapered hand file used to enlarge, smooth, or finish the inside of round holes and curved surfaces. Its slender circular cross-section, narrowing from butt to tip, allows it to reach into openings that flat or half-round files cannot.
Plain English
A long, thin, round file shaped like a rat's tail. It is used to clean up or slightly enlarge the inside of round holes.
Context Anchor
Seen in aircraft maintenance and repair work when a small hole or curved opening needs to be cleaned up by hand.
Derivation
Named for its resemblance to a rat's tail — long, round, and tapered. The shape gives the tool its name and tells you exactly what it is good for: working inside round openings.
Why Pilots Care
Proper use prevents stress risers or cracks that could lead to structural failure in flight-critical components.
Intuition Check
Do not picture a flat file or a document file. A rattail file is round and tapered, so it works inside holes and curved areas.
Example Sentence 1
The mechanic used a rattail file to deburr the rivet hole before installing the new skin panel.
Example Sentence 2
After drilling, he used the rattail file to remove the sharp burrs inside the tube before installing the fitting.