The Omnigrip 6.5in square has a diagonal line for triangle cuts; the ruler has extra 1/2in on two sides for seam allowance. Omnigrip square rulers are used for secondary cutting of strips, and to square up finished quilt blocks. Use for quilting, sewing and crafts - or any DIY project that calls for cut fabric. Omnigrid's® best selling small square, this multi-purpose ruler is a must have for every quilter. Foundation piecers love it for trimming seam allowances and squaring up their finished blocks. It is a perfect template for 6'' finished blocks, common in baby quilts, because it includes a 1/2'' seam allowance.