DG Performance 98-51375 - Quiet Insert 1.375" 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