Neighbor Hater Mufflers by Cobra are not for the faint of heart. These are an aggressive slip-on muffler, for those who think loud just isn't good enough. Each muffler starts as a round 3-inch tube, then bell out to 3.5-inches. It presents an aggressive and classic design at the rear. The muffler tip is then rolled to give it a clean, finished look. Internally, these NH mufflers have a perforated core with strategically spaced holes. This is done in order to produce an aggressive bark. At the end of the baffle is a trumpet shaped inner tip that works in harmony with the belled end, creating a unique look.