The Arundel Tri Clamp is simple device which clamps to the seat post instead of the seat rails, and it fits virtually all seat post shapes. No one else makes one like it. Triathletes popularized this behind-the-seat method of carrying water due to their need to hydrate like crazy, since once the bike ride was over, it still wasn’t over. It’s common to use two reserve bottles behind to dump into the front bar-mounted bottle, the one with the giant straw attached. The key to the Arundel Tri Clamp is the use of a ”V-block” design with convex inside surfaces. This helps it fit a variety of seat posts. Round or aero shaped; it doesn’t matter. By tightening the 6mm mounting screw, the Tri Clamp will stay securely fastened, while allowing for some shock absorption. Athletes benefit in several ways: The Arundel Tri Clamp fits well and remains secure, the bottles are easy to reach and it doesn’t cost an arm and a leg.