Design Nomenclature / Form & Geometry
Fillet
Also called round, radius, blend, edge round
This entry has not been translated yet and is shown in English.
A rounded transition replacing a sharp edge, generated by rolling a circle of fixed or varying radius into the corner and trimming both faces back to where it touches. Tangent to both surfaces by construction — G1 at minimum. It removes the stress concentration at an interior corner, so it is a structural feature before it is a cosmetic one.
In practice
In machining a fillet is specifically the concave interior round — material added at a corner — and a round is the convex exterior one. DCC tools call every edge treatment a bevel and let a profile setting decide which you get.
Not to be confused with
Origin
French filet, a thread or narrow band — the same word as the cut of meat. It named the narrow flat band in a classical moulding long before it named the round in the corner of a casting.