The try square is a tool consisting of a metal blade set at a 90 degree angle in a wooden handle. It is used to check for accuracy of the corners and joints, mark lines at right angles to edges and to check for perpendicularity of two parts. A try square has an accurate 90 degree angle on both it’s inside and outside edges.
To check a piece being planed for square, plane one face of the piece square, and mark it as the Face Side, from which all measurements will be taken. Then, press the wood handle of the try square against the face side; if the inside edge of the metal blade completely touches the adjacent edge, then the piece is square. An edge is then marked as true, as the Face Edge, once it has been checked with the try square.
To check an inside angle, such as a picture frame corner, put the try square’s heel into the angle. The blade’s edge should completely touch the other half of the corner joint.
Some try squares have a wooden stock, or handle, whose top edge is cut to an angle of 45 degrees. This can be set against the edge of a piece to mark off a line at a 45 degree angle.
Another type of try square is made completely from metal; this is called an Engineer’s Try Square. Both their blades, which can be from 3 to 42 inches long, and their stock, which can be from 3 to 21 inches in length are made of metal for greater accuracy. They are used to check metal workpieces for 90 degree angles and laying out work in engineering workshops, as well as in home metal workshops.
There is also a tool called an Engineer’s Sliding Bevel which is basically a try square which has an adjustable angle. It is also made entirely of metal, but has a knurled nut fastening the blade and stock which can be loosened or locked in order to adjust the angle. It is used to check or mark off angles of metal.