Kerker claims that, due to use of the Kerker designed K3 baffle core, these High Volume Slip-On replacement mufflers will add extra Horsepower to your motorcycle. They are 3 1/2" (89mm) in diameter and sold without end caps, giving you a choice of 17 different styles of SE series end caps to top them off and match the styling of your bike. When, at a later time you want to change to another style end cap, you simply buy another bolt-on end cap. SE Series mufflers bolt to the stock mountings in minutes and are sold in sets of left and right. SE series end caps are sold each and listed separately.