A T-square is a technical drawing instrument used by draftsmen primarily as a guide for drawing horizontal lines on a drafting table. The instrument is named after its resemblance to the letter T, with a long shaft called the "blade" and a short shaft called the "stock" or "head". T-squares are available in a range of sizes, with common lengths being 18 inch, 24 inch, 30 inch, 36 inch and 42 inch. In addition to drawing horizontal lines, a T-square can be used with a set square to draw vertical or diagonal lines. 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 are also used in various industries, such as construction. For example, drywall T-squares are typically made of aluminum and have a 48 inch tongue, allowing them to be used for measuring and cutting drywall. In woodworking, higher-end table saws often have T-square fences attached to a rail on the front side of the table, providing improved accuracy and precision when cutting wood.