There are many different types of metal files on the market, so we'll outline the most popular shapes. It is convenient to use the round files, which have teeth all around, to enlarge round openings. The three-square or taper files have two sides for cutting and one for smoothing. Many people use it for sharpening the teeth of a variety of tools. Finally, there are half-round files. These are half-flat and half-curved, while the square shape has four sides. In addition to the flat and mill files, as can the flat file and mill file. They are all cutting tools with teeth aligned parallel to the surface.