This ruler is an excellent square-up tool; it features a 1/2" seam allowance on 2 sides. Iit is used for cutting triangles and borders, and to cut and square blocks 9.5" and under when quilting. In general, Omnigrid square rulers are used for secondary cutting of strips, and to square up finished quilt blocks. You can use with a rotary cutter or a straight-edge blade. It has a diagonal angle line and edge markings for accurate measuring. The laser cut edges allow for smooth, deep cutting. The patented double-sight lines show up on light and dark fabrics. It is made from heavy-duty durable acrylic material with left- and right-hand numbering and angle system.Details:9.5" x 9.5"Laser cut edgesDouble-sight linesAcrylic