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.