Valdora's double hydro rack attaches horizontally to all round standard saddle rails and keeps your bottles and CO2 cartridges out of the wind, thus reducing drag. This behind seat bottle cage rack attaches onto the horizontal section of saddle rail. See images for explanation. This rack will not attach to the vertical portion of the saddle rail. Included is a removable bright LED tail light! Steady flash, slow flash or constant light. Excellent for morning and evening rides. 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 and and bright red LED tail light. Bottle cages and inflator can be added. Everything you need to train and race with confidence! Two threaded holes that will accept CO2 cartridges included! 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 - Alloy rack and LED light only. Bottle cages NOT included unless you select an option that includes additional accessories.