Originally Posted by
gear freak
this is by no means a comprehensive list. generaly the high end french bikes built of reynolds tubing (even though there are quality french tubes) like the peugeot px -10 or motobecane le champion these would have unthreaded simplex dropouts. huret used to make a nut that allowed you to mount a nouvo record in a simplex dropout. a more elegant solution was to tap out the dropout, i used to work in wakefield, ma & there was a shop that did retail sales of metric taps & dies, you will still need to file a stop. this option is probably more viable when consider how much trouble you would have finding the huret nut. i do not have any details about this nut, in the 1970s one of friends in the club used to ride a px-10 with a nouvo record rear derailleur & i haven't seen guy minnick in 25 years.
Huret made an adapter that would allow using a Huret derailer on a Campagnolo hanger, but I can't imagine a nut that would allow mounting a Campagnolo derailer on a Simplex hanger. A lot of material has to be removed to make the Campy derailer fit. It's not just to make a stop, you have to make clearance. It doesn't make sense that they would make an adapter to fit a competitor's derailer on another competitor's hanger.