Jeroen Belleman wrote:
. . .
It's one of my long-time gripes about coaxial connectors that N and
BNC series of the two impedance levels are sufficiently compatible
to mate together, but not enough to do so without damage. In a lab
with someone ignorant of this fact, it's a source of endless trouble.

All the 75 ohm BNC connectors I have, have the same diameter center pin
in the connection region as 50 ohm connectors. The difference is in the
thickness of the dielectric around the pin in the connection region,
being much thinner in the 75 ohm connectors. The pin of the 75 ohm
connector is smaller only where it's in solid dielectric at the bottom
of the connector.

Roy Lewallen, W7EL