The Topeak MTX Beam Rack is designed for MTB or heavy commuting use and can carry loads up to 20lbs. The improved QR mechanism makes the rack easy to attach to the seat post while the integrated rubber bungee cord secures your cargo. Also included with the rack is a safety reflector, RedLite mount for attaching a RedLite series rear light and a taillight mount for attaching other rear lights.Tough 6061 T6 Alloy ConstructionHinged Seat Post Clamp With Alloy Release LeverIntegral Bungee CordOne Size Fits All Seat Posts (25.4 - 31.8mm)(Shims Included)20lb Carrying CapacityWeight: Normal (S/M) 693g / Large: 696gSize: Normal (S/M) 54 x 12 x 10cm / Large: 51 x 12 x 11cm