Dual Muffler Systems require TWO Spark Arrester Kits. Available as optional Spark Arrester on applications not originally equipped with a Spark Arrester. Spark Arrester Insert. Kit Includes.
Although it is not printed anywhere online, the spark arrestor apparently builds up a fair amount of heat which shortens the life of the dampening material, and the carbon fiber sleeves will start to deteriorate. I found this out after the vague statement on the included instructions, followed by hours of research online. So if you have a carbon fiber sleeve and wish to use this, do some research first, because yoshimura straight up says don't do it. Otherwise it's a well designed product with excellent tolerances, fits perfectly and includes installation hardware.