There are many fine teeth and strips on the surface, which are hand tools used to file the workpiece. It is used for micro processing of metal, wood, leather and other surface layers.

The application of the file is very early, and the oldest file found is the bronze file of Egypt around 1500 BC.

Modern files are generally made of carbon steel by rolling, forging, annealing, grinding, cutting teeth and quenching. The file is made of t12 steel, which has a hardness of 62~64 after surface quenching.
There are many varieties of files.

①According to the purpose, there are: ordinary fitter files, used for general filing processing; wooden files, used for filing soft materials such as wood and leather; plastic files (assorted files), used for filing small and fine metal parts , There are many files with various cross-sectional shapes to form a set; files for sharpening woodworking saws; special files, such as flat and bow shaped files (special files) for repairing special shapes. There are two types of straight and curved files.

②Files are classified into flat files (flat files), square files, semicircular files, round files, triangular files, diamond files and knife-shaped files according to their cross-sectional shapes (see figure). Flat files are used to file flat surfaces, external circular surfaces and convex arc surfaces; square files are used to file square holes, rectangular holes and narrow flat surfaces; triangular files are used to file internal angles, triangular holes and flat surfaces; semicircular files are used to file concave arc surfaces And flat surfaces; round files are used to file round holes, concave arcs and ellipses with smaller radius.

③Files are divided into single-grain files and double-grain files according to the file pattern. The teeth of the single-grain file are inclined at an angle to the axis, which is suitable for processing soft non-ferrous metals; the main and secondary file patterns of the double-grain file are arranged in a crossed arrangement, which is used for processing steel and non-ferrous metals. It can divide wide filings into many small sections, making filing more brisk.

④Files are divided into No. Ⅰ ~ Ⅴ according to the number of main file lines per 10 mm length, among which No. Ⅰ is coarse-tooth file, No. Ⅱ is medium-tooth file, No. Ⅲ is fine-tooth file, and No. Ⅳ and Ⅴ are polished files. , Respectively used for roughing and finishing. The diamond file has no file pattern, but a layer of diamond powder is electroplated on the surface of the file to file hardened metal.