Profile Design Aqua Rack ii Dual Water Bottle Cage Co2 Cartridge mount Seatpost mounted Matte BLKProfile Design Aqua Rack ii Dual Water Bottle Cage with Co2 Cartridge mount: Seatpost mounted Matte Black. Rear mounted hydration system holds two bottles and attaches directly to the seatpost for easy hydration on the go. Full angular adjustment allows bottles to be rotated 6061 T6 aluminum construction Brackets included to mount two Co2 cartridges Fits 31. 6mm to 27. 2mm seatpost with shims (included) Includes two cages and 6061 T6 Aluminum clamp