They are called skip blades. You take your ruler and your skip blade that will fit on the 45mm rotary cutter, stay about a ½" inside the raw edge and place on the mat and roll. Makes minute/small holes to crochet an edge around the fleece. The holes are evenly spaced. We can take small remnants of 18" square, use the skip blade and crochet an edge around the fleece and the size is perfect for NICU preemies. You can do any size but a great way to use the remnants we find at Joann's for a song and a dance.