The zig zag foot with ankle set has a snap on foot for sewing over rises at the beginning of or in the body of your fabric. Simply tilt the foot and pull the button to set the foot. When a rise is encountered, the foot automatically realeases on it's downward slope. No more getting stuck at a rise or uneven stitches on the down side! This is also a great item to have on hand as a replacement for a lost or damaged ankle.