The Speed Square is designed for fast, accurate layout and cutting of angles for rafters, bracing, trim, cabinets and general wood work. It's a framing/try/miter square, saw guide plus protractor. One-number (roof pitch) reference is used for both common and hip-valley rafter scales. Includes pocket-size booklet that explains basic roof. Construction with diagrams, roof formulas, rafter tables and conversion charts. Made of tough, polypropylene plastic.