The Big 12 Speed Square is a 12 in. version of the Swanson Speed Square with added features for building stairs. This innovative tool is not only a Rafter Square, but it also combines 7 tools into 1: 1. Try Square, 2. Miter Square, 3. Saw Guide, 4. Line Scriber, 5. Protractor, 6. Out-of-Square Corner Angle Finder, and 7. Stair Layout Square. The Big 12 Speed Square is die-cast for durability and accuracy. Made of heavy-gauge aerospace aluminum alloy, it is built to last. Black-filled gradations stand out against a matte finish for easy reading and are simple to use with the Swanson 1-Number Method of rafter layout. This model includes the Swanson Blue Book for Roof and Stairway Layout as well as the Layout Bar for use in determining out-of-square corners when building stairways. The Swanson Speed Square is our most popular product and remains the most trusted square of its kind. Look for the Diamond cutout for genuine Swanson products.