The tool in the image is a speed square, a triangular-shaped measuring instrument made from plastic or metal. It combines the functions of a try square, miter square, protractor, line scriber, and saw guide in one compact tool. Typically used in carpentry, the speed square is invaluable for making quick, precise marks for cuts on dimensional lumber. The flat base allows it to sit steady on lumber, while the lipped edge can hook onto the material for consistent measurements. Its various scales enable carpenters to measure and mark angles for roof rafters, cross cuts, and other construction-related tasks efficiently. This tool is favored for its durability, ease of use, and versatility in various building projects.