Easy, bolt-in sound reduction for 3" HP-Plus® mufflers. Takes off 4dB at idle and improves low-end torque - minimal loss of top-end horsepower. The machined discs with tapered bosses fit into each end of the patented resonator near the exit end of the mufflers and are retained by the supplied bolts and nuts. This kit is designed to use with three-ball style resonators that are 6.50" long. Will also fit most other mufflers (four-ball style resonators) if 1/4"-20 x 11.00" threaded rods are substituted for the supplied bolts. Installation requires removal of the mufflers. Kit includes machined discs and (2) 7.50" 1/4"-20 bolts and two prevailing torque nuts. Made in the U.S.A..