The Omnigrid 8 half square triangle ruler is used to create half-square triangles for finished quilt blocks up to 8 . It has seam allowance calculations included in the measurements and is easy to manipulate for smaller triangles when quilting. The patented double-sight lines show up on both light and dark fabrics and the laser cut edges help create a smooth deep cut. It is best used with a rotary cutter or straight-edge blade.