Use the Omnigrid Right Triangle to create 1/2 square triangles up to 8″, seam allowances included. Omnigrid Rulers are the nomber one selling quilting ruler in the world. They are preferred by professional quilters & teachers all over the world. They are guaranteed to last longer than other rulers. They are the only ruler to maintain +/- .002 inch accuracy. Omnigrid’s patented and trademarked (black and yellow) double sight line make for easy reading and measuring on light and dark fabrics. Markings make right or left handed use easy. Omnigrid Rulers have grid markings throughout. These rulers are made of heavy-duty, premium quality acrylic and laser cut for a smooth edge.