Identify a 2.9mm Fixed Attenuator from 2.4mm Fixed Attenuator

With the push to 5G by wireless cellular providers, lab benches are now being occupied with a greater number of high frequency fixed attenuators with 2.9 mm (aka 2.92 mm) and 2.4 mm RF connectors.  It is important to be able to tell these RF connectors apart because 2.4 mm and 2.9 mm connectors will damage each other if mated together.  2.9 mm connectors operate up to 40 GHz.  2.4 mm connectors operate up to 50 GHz.  There are notable visible differences between SMA, 2.9 mm and 2.4 mm connectors.  SMA and 2.9 mm connectors can be mated to each other without causing damage.  Their connector threads are identical and their male/female pin diameters are mechanically compatible.  The obvious difference between a SMA female and a 2.9 mm female is the dielectric.  SMA female has PTFE dielectric and 2.9 mm has an air dielectric.  2.4 mm connectors are not compatible with SMA or 2.9 mm.  The 2.4 mm connectors have a different thread and male/female pin diameters are 56% smaller.  The RF specifications for fixed attenuators that work up to 18 GHz, 40 GHz, and 50 GHz vary greatly.  The RF specification differences can be seen with these three low power fixed attenuator models:  50HFFA-xxx-2/18 SMA (DC-18 GHz), 50HFFB-xxx-2/40 2.92mm (DC-40 GHz).