Omnigrid Omnigrip Non-slip Rulers are made from a durable, premium quality acrylic plastic and laser cut for a smooth edge that allows for easier, deeper cutting of fabric layers. The patented non-slip backing literally "grips" your fabric to hold ruler in place during cutting. The 5 1/2 x 5 1/2 inch ruler is used for secondary cutting of strips, and to square up finished quilt blocks. The ruler has extra 1/2 inch on two sides for seam allowance. 45 degree diagonal line is great for triangle cuts, markings for half-squares and quarter-square triangles.