Tools are simple machines. When they become complicated they are called machines, and machines acting with great power take the name of engines.

Workshop tools are divided into two classes, hand-tools and machine tools. The former class includes hammers, chisels, files, ratchet braces, spanners, etc. The latter class includes lathes, planing, shaping,drilling, and slotting machines, used in the fitting shop; and punching and shearing machines, bending rolls, and steam hammers, used in the smith's shop. The compressed air attachment (Fig. 8) is a good example of a power tool.