Johnson's 16 x 24 in rafter square is everything a builder needs to get the work done quickly, efficiently and accurately. It includes graduations in 1/8 in, 1/10 in, 1/12 in and 1/16 in as well as octagon scales, rafter tables, brace tables and board foot tables, making it useful for any number of different jobs. And those graduations and tables are permanently stamped so you'll never worry about them fading or wearing. This rafter square's aluminum construction makes it conveniently lightweight while also keeping the tool safe from rust.