Are these
(R&S) the threaded aviation/military connectors?
No, those threaded things form a diverse family, and go under the
names of AN3100s, MS connectors, and so forth.
The old R&S connectors are the big "pin and sleeve" types, with older
models in metal enclosures. The new ones are plastic, color coded, and
in the UK are called "Commando plugs". They are often seen at marinas,
as they are available in water tight enclosures.
My HP2116C came with a threaded-and-keyed-housing
connector with 3
round
pins in a triangle, one being longer than the others.
One of a large family of connectors with various housing diameters and
number of pins, which I've always taken to be primarily an aviation
and
military-use family, but never known the name of.
Originally AN310x, with x signifying straight/angle/chassis/cable
options. The system was formed around 1941 (I think), in order to
standardize the US military's connector situation.
I don't know if it was a special order on the
HP2116 or standard
(never seen
it on other HP equip), but I replaced it rather than try to find the
mate.
Those three pinners in various sizes are quite common.
Ah-ha, I've found the Amphenol catalog for the MS3100 series and
matched up the part number for the 2116 connector. Can't say I'm ready
to order the plug, but it's nice to know what it is for future ref.