Simply slide on a line before you tie on a lure or fly. Action Discs add the natural swimming action and vibration that has become increasingly important to catch trophy fish in heavly fished waters. They produce truly unique action in light lures or flies that normally rely on the movement of the material or skilled manipulation by the angler to bring out the best. * NOT recommended for use with fluorocarbon leader or line. Fluorocarbon leader under 20lb test does not stand up well to constant bending caused by the ActionDisc, it has a tendency to break much like bending a coat hanger wire back and forth repeatedly.