DUO Cool Down 27.2mm BMX Seatpost Extender - Black 21t The rear uses a 16t+

The rear uses a 16t+ freewheel (not included) and a standard 6B rotor (not included)

Nickel-plated sprocket ring

Thickness: 4

and for good reason

making it an aesthetic yet highly functional lightweight sprocket

DUO Cool Down 27.2mm BMX Seatpost Extender - Black 21t The rear uses a 16t+The DUO Cool Down race post is designed for cooling down after a fast lap around the track. Racers remove their race seat & post from their bike, drop in the DUO Recovery post into their frame, then insert their race post in the top. This creates road bike type sizing for efficient pedaling while seated. Perfect for training rides aboard a race bike too. Aluminum construction, 1 piece design Black anodized finish w silver etched DUO capsule pattern