A year or two or three ago I acquired a Campy Nuovo Gran Sport RD. I've been wanting to put it on a particular bike which has Campy DO's but it doesn't want to thread on. I've mounted a Suntour Cyclone II on the bike and it went on easily. The Campy RD just doesn't like the threads. It will go on no more than one turn and isn't happy about going on that much. I don't want to force it with a big wrench.
The threads do not appear damaged. They appear to be the same as various Suntour RD's in my parts stash, but perhaps not.
Might Campy have made a version of this RD with, say, French threads?
It's not an earth-shattering question, but that RD seems to be unusable for now.