If you go look at this listing you can see the nuts that the non threaded stud use. I don’t have any information on the threaded ones sorry.

Look at this on eBay

MoPar 70 71 Dodge Dart Demon Fender Extensions With Chrome 1970 1971 1972

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F123892192534

eBay-cdwmotorsports