If you have a mixture of 50 Ohm and 75 Ohm N series adapters or connectors, it would be best to be mindful that the RF pin and socket diameters are different between the 50 Ohm and 75 Ohm series.
The RF pin on the male and the socket on the 75 Ohm series will have a smaller OD and ID than the 50 Ohm series. Plug the 50 Ohm male into the 75 Ohm female and you can possibly damage the 75 Ohm female as the 50 Ohm RF is to large.
If you plug the 75 Ohm male pin into a 50 Ohm female socket, it will fit but may not perform as it will not be tight and your results will be unstable and damage may occur from arcing.