Most of the tools a machinist or tool-maker uses have nothing of great difficulty or mystery connected with their making. Any good tool-maker, if necessity demands, would feel competent to make for him self a twist drill or a micrometer caliper, even though these tools are seldom made for personal use, but are almost invariably purchased.

There is a different feeling in the case of files, however.  A good file is treasured by the man who owns it. He looks upon it with friendliness and respect as well, for while he can buy files by the thousand (good, bad and indifferent) from people who make a business of making them, he would not be able to make one himself.

The matter of cutting those fine teeth, so well formed and regular, and yet so delicate as to be in the finer sizes almost invisible, and afterwards the hardening of the tool to the proper degree without injuring the sharpness of these multitudes of little teeth, he feels to be beyond the range of his ability.

File makers, in general, have rather catered to this idea of mystery.  Their shops are surrounded by high fences and the visitor gets no further than the office.  Their catalogues are full of little hints and suggestions of the complicated special machinery used, and the secret and mysterious formulas and processes followed in the annealing and hardening departments.