The AcuFeed Flex system allows you to sew through many layers of fabric very easily without slipping, or warping the layers. You won't have to worry about anything, even with a full sized quilt project! The beauty of the AcuFeed Flex system is the versatility of the feet. They slide in and out like the snap-on presser feet for the machine giving you more options for all of your stitching. The single size is more narrow than the twin.