Machinist square

A machinist square or engineer's square is the metalworkers' equivalent of a try square. It consists of a steel blade inserted and either welded or pinned into a heavier body at an angle of 90°. In the accompanying image, there is evidence of pinning at the intersection of the blade and body: the heads of three pins are visible as dark circles. A small notch has been added to the inside corner of the square to prevent small particles from accumulating and affecting the square's reading, by causing it to rock. This notch is typical of machinist squares.