Definition
A hand file with one flat side and one curved (rounded) side, used in aircraft maintenance to shape, smooth, or enlarge curved surfaces and holes while also being able to work flat surfaces with the opposite face.
Plain English
A metal-shaping tool shaped like a half-circle in cross-section. One side is flat, the other is rounded, so it can work both straight edges and curves with a single tool.
Context Anchor
Seen in aircraft maintenance and shop work when fitting parts, smoothing rough edges, or shaping a curved opening.
Derivation
Named for its cross-sectional shape: if you cut a round file lengthwise down the middle, you get a 'half round.' The flat side comes from the cut, the curved side from the original round profile.
Why Pilots Care
Using the right file helps a mechanic shape or smooth a part without removing too much material or leaving a rough edge that could lead to cracking or poor fit.
Intuition Check
A half-round file is not a file that is half-size. It is called half-round because one face is rounded and the other face is flat.
Example Sentence 1
The mechanic used a half-round file to smooth the inside edge of a freshly drilled inspection hole.
Example Sentence 2
After fitting the new bracket, he reached for the half-round file to contour the curved surface to match the fuselage.