An engineer's file is used for smoothing metal or enlarging holes in metalwork. Use a half-round file for smoothing curved surfaces and a flat file for flat surfaces. For enlarging holes such as an aerial hole in a car body, use a round (or rat-tail) file, which is thin and tapered.

Engineer's files are generally single cut - that is, with parallel, not criss-crossed, teeth. Depending on the density of the teeth - generally 26, 36, or 60 per 25mm - their cut may be bastard (medium coarse), second (medium smooth) or smooth. The denser the teeth, the smoother the cut.

Files are often sold without handles, which can be bought separately. For safety always fit a permanent handle to an 8 to 10in. file; do not use the same handle for different files. Store files carefully, not jumbled with other tools, such as spanners, or the cutting edge may be damaged.

A file is a metalworking, woodworking and plastic working tool used to cut fine amounts of material from a work piece. It most commonly refers to the hand tool style, which takes the form of a steel bar with a case hardened surface and a series of sharp, parallel teeth. Most files have a narrow, pointed tang at one end to which a handle can be fitted.

A similar tool is the rasp. This is an older form, with simpler teeth. As they have larger clearance between teeth, these are usually used on softer, non-metallic materials.

Related tools have been developed with abrasive surfaces, such as diamond abrasives or silicon carbide. Because of their similar form and function, these have also been termed 'files'.

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