Muffler Black W/Bt Bolt4" Slip on MufflerFeatures advanced acoustical tuning technologies for deep rumbling sounds 4" round muffler front expands to 4. 5" diameter near the rear Comes with a 3" core encased in proprietary Cobra sound tuning materials with specific acoustical dampening and thermal insulation properties; deep bass notes are made possible because of class leading resonance absorption and prevention Satin black muffler includes a custom heat shield to smooth