Corner Cutters are cut from clear 1/8" acrylic (paper still affixed for better pictures - not exactly as shown). Use a 45mm blade to cut to the inside corner, even with 2 (two) layers of fabric, which allows you to cut more than 1 (one) corner at a time, for even more time saving.
Corner Cutter FAV cuts box corners 2", 2 1/2", 3" and 3 1/2" corners.