Spark Arrestor Insert. To this day - everything Yoshimura does revolves around building fast machines and winning races. What motivated Pop's Yoshimura over 50 years ago is the exact same thing that motivates Yoshimura today. Racing and winning. There is no other endeavor that they would rather be engaged in. Replacement U.S.F.S. Approved Spark Arrester for off-road mufflers. Available as optional spark arrester on applications not originally equipped with a spark arrester. Kit includes: Spark arrester insert. End-cap collar. Set screw. Note: For Yoshimura RS-4 Exhaust. 1.375" diameter.