Speed square

A speed square, also called a rafter square, rafter angle square, and triangle square, is a multi-purpose triangular carpenters' tool used for marking out. Its functions encompass many of those offered by combination squares, try squares, and framing squares. Carpenters use it to make basic measurements and mark lines on dimensional lumber, and as a saw guide for short 45 and 90 degree cuts.

"Speed Square" is a registered trademark of the Swanson Tool Company in the United States, though the term is often used generically for squares of this type.