Cobra EL Diablo 4 Slip-On Mufflers For Harley Fxfb Cobra has brought their take on a pair of Slip-Ons for the new Softail Fat Bob model. Cobra has fitted their El Diablo 4 slip-ons and look as if they were meant to be on the bike originally. Features Utilizes a cone style muffler body Expands to 4 at the rear Mechanical baffling system offers an increase in sound and power Billet aluminum reverse cone tip finishes off the rear Tip is power-coated black, with Cobra etched on top