The Omnigrip 16-1/2” Square Ruler is great for squaring up blocks and short strips. It has a diagonal line for triangle cuts, and an extra 1/2" on two sides for seam allowance. Features: patented non-slip backing to hold the ruler in place during cutting; edge markings for accurate measuring; laser cut edges for smooth, deep cutting; patented double-sight lines that show up on light and dark fabrics; left-and right-hand numbering and angle system, and is made of heavy-duty acrylic material.