Omnigrid Omnigrip Non-Slip Neon Rulers are made especially for quilting sewing and crafting projects. Use with rotary cutter or straight edge blades. Made with a unique numbering and angle system and may be used with either right or left hands. Grid in both Neon Green and Black so that it will be visible on both dark and light colored fabrics. 20.5 Square- For cutting squaring and setting blocks. 45° diagonal line for triangle cuts markings for half-squares and quarter-square triangles. Also has an extra 1/2 included on 2 sides for quilting seam allowance.