It is not only important that the workman should know the character and usefulness of the various materials, but it is also essential that he should be familiar with the steel square, which is the universal tool used to lay out the material. Figs. 16 and 17 show one side of one of the common squares in general use. The three parts are distinguished by special names, the tongue, the blade, and the heel. The longer and wider arm is the blade, the shorter and narrower arm is the tongue, and the point where the two arms meet is called the heel.

The numerous applications of the tool are given in detail under the subject of "The Steel Square."