Cobb’s patented and aerodynamically tested hydration mount attaches to the underside of the saddle versus the rails allowing for greater room for adjustment. Riders can attach either two bottles to the sides or one cage in the middle. There is a spot to screw in a CO2 cartridge. The bottle cages are not included, but include a small gear bag. The Rear Hydration Mount is only compatible with the Fifty-Five, Randee, Gen 2, and Plus 2 saddles.