Aluminium Seatpost for the 16,20, and 24" wheel Dahon folding bikes that use the 580mm x 33.9mm seatpost Length of Shim 80mm. This was designed to replace the Plastic pegged shims of early Dahons. There is no peg on these and Dahon recommended cleaning the inside of the seatube and using a spot or two of adhesive to prevent them sliding out when adjusting the seat height. Aluminium shims grip better, and also add strength to the frame in the area vulnerable to fatigue particularly with tall riders.