The PB Products Rig Rings of 5 millimeters are specially designed for use with mono main line. You first slip the ring over the main line and then mount the Hit and Run clip and tail rubber in the usual way. Where normally the loop of the leader is placed over the clip, you now knot the mono line to the ring. The ring thus takes over the function of the loop. Once you slide the ring over the clip, a perfectly functioning safety system is created.