To solve a problem of terrible work wherein there is a danger of cutting hands when a burr is not removed since processing of a steel plate easily generates the burr projecting at an acute angle on the cross-sectional tip at punching and cutting time, and must be relied on a sense of the hands for rounding the corner by removing the harmful burr by using a file in a present state.

A tool is formed by uniting flexibility and hardness surpassing a fixed idea that the file must be hard by combining several items by hardening a surface by a diamond coating similarly to the file by applying a recess- projection to a spring-like coil (a shape is a circular or elliptic shape) by a sand blast. The file is effective only in the pushing direction, and this file simplifies work of both push and pull by using bending of a spring so that even an unskilled person can effectively quickly remove the burr, can smoothly finish the rounded corner, and can work an inside surface of a hole.