Yoshimura RS-4 Exhaust Spark Arrestor | SA-13-K. Updated Version of SA-13-K, weldnut inside of insert makes installation/removal easierReplacement USFS Approved Spark Arrester for RS-4 Mufflers with "Turn-out" end-cap.Available as optional Spark Arrester on applications not originally equippe... - Yoshimura RS-4 Exhaust Spark Arrestor | SA-13-K.