This rear-mounted hydration system holds two bottles and attaches directly in front of 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 and extension