Red Shift Dual Piston Cam Chain Tensioners Fits 2007-Up Big Twin engines, 2006 FXD engines, and all 1999-2006 Twin Cam engines converted to hydraulic tensioner systems. Dual Piston Design Eliminates Chain Instability & Tensioner Shoe "Rocking" Facilitates Accurate Cam Timing Events for Both Cylinders & Tolerates Common Crankshaft Run-Out (Unlike Gear-Drive Cams) Improves Throttle Response, Acceleration and Across-The-Board Power Precision CNC Machined and Made From Superior Materials