Dritz Omnigrip by Omnigrid 16-1/2&rdquo; Square Non-Slip Ruler Patented non-slip backing to hold ruler in place during cutting Uniquely patented double-site lines that show up on light and dark fabric Right and left hand numbering and angle system Extra 1/2" for seam allowances Made of heavy-duty acrylic, laser cut to within .002 inch accuracy