The Omnigrid 6-1/2 x 6-1/2 ruler is a popular baby quilt block size; it features a 3 x 3 section of 1/8 grid markings and a 1/2 seam allowance on 2 sides; it is used for cutting and checking half and quarter square triangles. 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.