Used to extend the upper pannier "arms" if the existing "arms" are not long enough. They can be used by themselves to replace the current arms
or they can be bolted onto the current arms to "extend" them.
We stock 3 types of fitting sets, all 175mm long:
F4 & F4c are both straight extensions. F4c is completely straight, while F4 has a 12mm kink to it, allowing it to be used in an inside or outside fashion.
F1 is a 90deg extension. Once the extender is bolted to the other arm, the part that bolts onto the bike frame is now "flat", rather than upright.