I just wanted to let people that don't already know:
There are 2 models of the rear hanger.
a) The 2 screw model. This one uses two small bolts that thread into the tapped holes in the Campy dropout. This is the most common.
b) The single screw model. This one is specially adapted to fasten utilizing the window of the dropout. It uses a special tapped washer that inserts into the dropout window. This allows the installation of the Porta Catena system on Campy dropouts that don't have the integrated tapped holes. Less common than the 2 screw. I imagine, but don't know for sure, that this single screw model will work with other Campy-clone dropouts.
Marc Boral
Long Beach, CA