On Friday, February 23, 2018 at 10:52:49 PM UTC-8, wrote:
Do they sell a gauge to measure Coaxial Power Connectors?
AKA "barrel connectors".

Someone must have some sort of gauge to measure them....

None that I've found. The parts that are hard to measure, I generally just
give up and buy a few score of each nearby size. At a PPOE,
we kept notes on 'hits' when an important failure-prone connector matched
something we could order (didn't happen a lot).

If it were time-critical (and I couldn't find a junker adapter to clip a
pigtail from), I've got drill bit shanks down to #60 (~1mm), and modeling
clay, and a measuring microscope. The thing is, even if I DID measure
accurately, the 'nominal' sizes of commercially available mates would
still be a mystery. So, it's easier to keep a divider-box of a dozen sizes
of the males/females, with annotation as to what to reorder.