Extra Long is for mounting Topeak II Racks and Topeak MTX Tubular Racks for small framed bikes.
For BabySeat II Racks and MTX Tubular Racks (34.5 cm in length for small bike frames).
NOTE : If you have a small frame bike and cannot install Topeak rack or BabySeat in recommended position (2 or 3˚ from horizontal), please use the 34.5cm extra long mounting bracket arm for proper installation
