Whatever the size of the taper file, the shape is the same, as the file, in profile, is an equilateral triangle, meaning that each of its three angles is sixty degrees.
This also means that the file will simultaneously file both the front of one tooth and the back of the one facing it, leaving them both shaped to the proper angle.
The smallest files will sharpen saws with fine or coarse teeth, but the larger files will sharpen the larger- toothed saws more efficiently.
There is some argument as to whether single-cut or double- cut files are best (either will do), but for coarse (five to seven points or teeth per inch), a regular taper is suitable; for medium coarse (eight to ten tpi) use a slim taper; for medium fine (eleven to fourteen) an extra-slim taper; for fifteen or more, a double extra- slim taper.
An occasional wipe with a rag dampened with machine oil is good for the blade, too.
Over time, however, the best of handsaws, even those that are treated with proper care, get dull.
Look closely at the teeth: Are they all the same height?
If not, you will need to perform an operation called jointing.
Simply clamp the saw in a vise, using wood blocks as a backboard to hold the spine of the saw rigid.
Clamp the saw, blade up, between two straight pieces of hardwood stock in a wood vise or purpose-made sharpening vise.
The clamping arrangement should grip the sawblade close to the cutting edge, with the gullets (the troughs between the teeth) not more than a quarter of an inch from the jaws, to ensure that the blade is held rigid.