This ring is meant to replace the old, and quite frankly useless, hop stabilization ring we've all come to know and love. It fits snugly over your barrel and wedges itself just inside the front of your hop unit vastly increasing stability between the hop unit and the barrel. The O-ring mod further enhances the effect by improving seating of the ring and further stabilizing your barrel. Its a small idea that fixes a big problem. Get the most out of your gun, don't let your accuracy components flop around. This is a 5 pack of self adjusting rings which fit all ~8.6mm OD (standard) airsoft barrels.