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A T-square is a technical drawing instrument used by draftsmen primarily as a guide for drawing horizontal lines on a drafting table. It may also guide a set square to draw vertical or diagonal lines. Its name comes from its resemblance to the letter T. T-squares come in varying sizes, common lengths being 18 inches (460 mm), 24 inches (610 mm), 30 inches (760 mm), 36 inches (910 mm) and 42 inches (1,100 mm).
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.
A T-square has two components—the long shaft called the "blade" and the short shaft called the "stock" or "head". 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.Tee square can be use to draw horizontal and vertical line without a ruler.
- United States War Department (1940). Topographic Drafting. U..S. Government Printing Office. pp. 27–28.