US Patent 7044874 Bicycle rear derailleur

A derailleur includes a base member for attachment to a bicycle frame and a movable member supporting a chain guide such that the chain guide moves laterally to shift a chain among a plurality of gears. The base member has a laterally inner surface and a laterally outer surface, and it includes a projection extending from one of the laterally inner surface and the laterally outer surface for engaging a corresponding recess in the frame.