"The Firefly Glow-Y Block Ruler is an easy-to-use, multi-function ruler that makes IDENTICAL Quarter Square Triangle Units with NO bias edges. These QST Units are used in creating 1in to 6-1/2in Y Blocks and Quarter Square Triangle Blocks along with over 50 other blocks.Cathey Marie Designs has found the solution to wasted mirror image units and wonky bias edged blocks! This ruler can be used to cut squares, mark stitching lines and square blocks. A variety of great Y Block Ruler patterns are available. The design possibilities are endless assuring many more fun projects to come.