T-square

T-square

An old T-square.

A T-square is a technical drawing instrument, primarily a guide for drawing horizontal lines on a drafting table. It is used by draftsmen. It is also used to guide the triangle that draws vertical lines. Its name comes from the general shape of the instrument where the horizontal member of the T slides on the side of the drafting table. Common lengths are 18", 24", 30", 36" and 42".

T-squares are also used to measure and cut drywall. Drywall T-squares are typically made of aluminium and have a 48-inch (1,220 mm) long tongue.

Higher-end table saws are often equipped with T-square fences. These table saw fences are attached to a rail only on the front side of the table unlike traditional fences which clamp to both the front and the rear of the table.

The top of the T-square hangs off of the drafting table and is called the head, whereas the blade is the part that stays on the drafting table. The T-square usually has a transparent edge made of plastic which should be free of nicks and cracks in order to provide smooth, straight lines.

T-squares have been used to cut drawings created by draftsmen since the inception of the instrument.^{[citation needed]} Although this is inadvisable, since one may cut the T-square in the process, rendering T-square useless since it would not have a straight edge.^{[citation needed]}