Campagnolo Gran Turismo rear derailleur - Appears to be NOS.

This derailleur comes complete with the mounting nut that is required for mounting. These derailleurs use an upper pivot spring as well as the lower one. Because of this design, it cannot be just bolted to the hanger. It must be held in place by a nut on the backside of the hanger. Trying to improperly install tends to lead to a broken upper pivot spring. This is the main point of failure for these derailleurs. Also the plastic sleeve that retains that same spring gets old and splits causing the spring to loosen and break the end off. The sleeve can be replaced with a custom machined aluminum replacement but the spring itself is almost impossible to find. This is a beautiful and iconic derailleur, but it was short lived. Thank you for looking.