S&S Off Road Division Muffler Inserts For Power Tune XTO Exhaust - Front/Rear Plug The S&S Muffler Insert Plugs offer enhanced tuneability by reducing flow from one outlet, thereby allowing for more customization options. Features: Power and torque tuning Tone and sound adjustment Ease of installing 304 Stainless construction 3.5mm Holes, Plugged, 1.75