I just ran across this tidbit:
Q: How can I tell the difference between a 50 and 75 Ohm N connector? A: You can tell the difference by the center pin. A 50 Ohm connector has a pointed pin. A 75 Ohm has a rounded pin.
I've always looked at the center conductor to shield (not ferrule) distance to make sure I had a 50-ohm version. I don't have any 75-ohm versions lying about the shack. Can anyone else confirm this?
I recall, back in my RF engineer days, that we had a whole box of 75-ohm N connectors which were marked with bright red paint. Woe to the junior engineer who coupled the 50-ohm and 75-ohm version, which would bend the center spring fingers on the female connector apart permanently.
One can also kill a female N connector by mating it with a male PL-259. I have not done this myself, but I knew someone who did this twice on his fancy new antenna analyzer and wondering why everything was such a poor match. :-)
--- Zach N0ZGO