Valdora's behind saddle hydro rack attaches to all round standard saddle rails and keeps your bottles and CO2 cartridges out of the wind, thus reducing drag. It is a behind the saddle hydration system that is must have for racing or training rides. An extra bottle to replenish your between the aerobar bottle during races. Maybe a shot of the hi carb nutrition that you will need. Or a modified bottle to carry an extra tube, tools, patch kit....whatever you can think of, carry it here. A competitor should not train or race without a Valdora hydro rack. Lightweight alloy, tough and easy to adjust. Includes hydro rack ONLY. This rack is what you need to train and race with confidence! Two threaded holes that will accept CO2 cartridges have been added to this latest model! We ship this product by USPS Air. Usually one business day for order fulfilment and 2-3 for it to reach your home or business. Not for use with carbon 7 x 9 mm (not round) saddle rails. Note - bottle cages depicted are for reference only.