A good tool-kit holds a number of files of various shapes. Some are flat, others half-round, three-sided, square and round. They are generally thickest in the middle, while their teeth are of various degrees of fineness and of different forms.

A file whose teeth are in parallel ridges only is called single-cut or float-cut. Such are mostly used for brass and copper. When there are two series of ridges crossing each other the file is double-cut, which is the. file best suited for iron and steel.

Rasps are files which have isolated sharp teeth separated by comparatively wide spaces, and are chiefly used for soft materials such as wood and horn.

Each of these three classes of files is made in six different degrees of fineness, the coarsest being called rough, the next middle, followed by bastard, second-cut, smooth and superfine or dead-smooth, each a degree finer than that which precedes it.

Files are usually made with the hand, file-cutting machines not having been as yet perfectly successful on account of the delicacy of touch required in the work.

The blanks, as the steel before it has teeth is called, are laid on the anvil and struck with the chisel, which rests obliquely on the blank, each blow raising a ridge or tooth. The strength of the blow depends on the hardness of the metal, and when one part is harder than another the workman alters his blows accordingly. When one side is covered with single cuts if the file is to be double cut he adds in the same manner a second series, crossing the others at a certain angle.

In making fine files a good file-cutter will cut upwards of two hundred teeth within the space of an inch. The files, except those that are used for soft substances, are hardened by heating them to a cherry-red color and then dipping them in water. They are then finished by scouring and rubbing over with olive oil and turpentine.