Hand tool file
A hand tool for filing, trimming or polishing the surface of an object by reciprocating friction. The file consists of a steel file body with teeth cut on the surface and a file handle, and the file handle of a large-scale steel file (also called locksmith file) is also equipped with a wooden handle. The shape of the file body is long, and its cross section is mainly flat, round, semicircle, square and triangle, which can meet the processing needs of workpieces with various surface shapes. Special purpose files can also be made into various strange shapes. On the working face of the steel file body of the file, there are countless sharp edge lines regularly hewn along the axis direction. According to the density of file teeth, files can be divided into three types: coarse file, medium file and fine file. Usually referred to as a smooth file with particularly fine teeth, it is used for dressing workpieces that need a fine and smooth surface. According to the processing object, the file can be divided into single file and double file. The files on the single file face are diagonally parallel or diagonally arranged along the center line, and are often used to file hardware and wood materials. The teeth on the working face of the double-grain file are arranged crosswise, and the tips of the teeth are generally inclined forward at a certain angle, so the file only has the function of filing in one direction.

Files are generally made of carbon tool steel, which is high in carbon content, brittle and hard. When making a file, the steel is first rolled into file blanks of various shapes, and then the teeth are cut on the file blanks after annealing. At first, the teeth of the file were cut by hand with a small flat chisel, but in modern times, the teeth are cut mechanically with a tooth cutter. Files with broken teeth can only be used after heat treatment and reaching the required hardness. Common files include locksmith file, plastic file, special-shaped file, clock file, saw file and soft material file. It is used to file the surfaces of lead, tin and other soft metal products, as well as nonmetals such as plastic, wood and rubber. The file line of soft file is arc single line, and the file leans forward greatly, so it files much more. This kind of file also includes wood file for carpenters and rubber file for shoemakers.