DG Performance 98-51000 - Quiet Insert 1.00" dia. - fits"R" and"O" Series Exhaust (1973-2012) Tune exhaust sound and power and reduce exhaust sound by 1 to 6 dBs on DG O-Series exhaust Easy to install by removing rear end cap and placing insert in front of spark arrestor Available in five sizes; smaller diameter inserts are quieter but more restrictive, larger diameter inserts are louder but less restrictive