Files come in a wide variety of sizes, shapes, and tooth configurations. The cross-section of a file can be flat, round, half-round, triangular, square, knife edge or of a more specialized shape.
Some of the common shapes and their uses: Hand Files are parallel in width and tapered in thickness - used for general work.
Joint Round Edge files are parallel in width and thickness, with rounded edges. The flats are safe (no teeth) and cut on the rounded edges only. Used for making joints and hinges.
Half Round Ring files taper in width and thickness, coming to a point, and are narrower than a standard half round.. Used for filing inside of rings.
Barrette files are tapered in width and thickness, coming to a rounded point at the end. Only the flat side is cut, and the other sides are all safe. For doing flat work.
Checkering files are parallel in width and gently tapered in thickness. They have teeth cut in a precise grid pattern, and are used for making serrations and doing checkering work, as on gunstocks.
Crossing Files are half round on two sides with one side having a larger radius than the other. Tapered in width and thickness. For filing interior curved surfaces. The double radius makes possible filing at the junction of two curved surfaces or a straight and curved surface.
Crochet files are tapered in width and gradually tapered in thickness, with two flats and radiused edges, cut all around. Used in filing junctions between flat and curved surface, and slots with rounded edges.
Knife files are tapered in width and thickness, but the knife edge has the same thickness the whole length, with the knife edge having an arc to it. Used for slotting or wedging operations.
Pippin files are tapered in width and thickness, generally of a teardrop cross section and having the edge of a knife file. Used for filing the junction of two curved surfaces and making "V" shaped slots.
Square files are gradually tapered and cut on all four sides. Used for a wide variety of things.
Triangle or "Three Square" files are gradually tapered and come to a point. Used for many things, cutting angles less than 45 degrees, etc.
Round or "Rat Tail" files are gradually tapered and are used for many tasks that require a round tool - opening holes, cutting a scalloped edge.
Round Parallel is similar to a round file, except it does not taper. Shaped like a toothed cylinder.
Equalling Files are parallel in width and thickness. Used for filing slots and corners.
Slitting Files are parallel in width with a diamond shaped cross section. Thinner than knife files and use for filing slots.
Pillar files are parallel in width and tapered in thickness for perfectly flat filing. Double cut top and bottom with both sides safe, these a long, narrow files for precision work.
Warding files are parallel in thickness, tapered in width, and thin. Like a hand or flat file that comes to a point on the end. Used for flat work and slotting.
A file's teeth can range from rough, coarse and bastard (meaning intermediate) to second-cut, smooth and dead smooth. A single-cut or mill file has one set of parallel teeth, while a cross-cut or double-cut file has a second set at an angle to the first. In Swiss-pattern files the teeth are cut at a shallower angle, and are graded by number, with a number 1 file being coarser than a number 2, etc.. Most files have teeth on all faces, but some specialty flat files have teeth only on the face or only on the edge, so that the the user can come right up to another edge without damaging the finish on it.
Dreadnought (curved teeth) and millenicut (straight teeth) both have heavily undercut, sharp but coarse teeth. Both can be used for rapidly removing large quantities of material from thick aluminum alloy, copper or brass. Today, the millenicut and dreadnought have found a new use in removing plastic filler materials such as two-part epoxies or styrenes such as those commonly used in automobile body repairs.