If you look at the website of Crescent Tools, the parent company of file manufacturer Nicholson, and search for files, you will get 415 results. With so many options, how does one sort out which metal file is best for the job?
Files come in a variety of coarseness and types of cut. American pattern files are available in three tiers of coarseness: bastard cut, medium cut, and fine cut. The cut can be either single or double; in the latter case, the second cut comes across the first at an angle. Files from RapidCut have diamond-shaped teeth and are used primarily for coarse work. The coarseness of the cut of most files varies proportionally with the length of the file—a shorter file will be finer than a loner one. The file length is generally measured by total length of the file minus the tang. American pattern files can be anywhere between 4" and 16" long.
Swiss pattern files have a much larger range of cut coarseness; 00 is the coarsest, 6 is the finest, and 0 to 4 are the most available. The coarseness of these files also varies with the length of the file. These files are shorter than American pattern files, generally between 2" and 8" long, and are often used for fine work.
What are the Different Shapes of Metal Files?
Flat Files
Files come in many cross-sectional shapes, but the most basic is rectangular. A parallel-edged flat file is simply called a hand file and an American flat file is slightly tapered. Both American and hand files come in the largest variety of sizes.
Some have what is called a “safe edge”—that is, an edge with no teeth. This allows the file to cut into a corner with-out damaging the adjacent surface. It is good practice to polish the safe edge with a diamond stone or other type of stone to be certain the safe edge has no cutting capability. Grinding a safe edge is not recommended because it is likely to draw the temper, or heat-induced toughening, out of the file.