One wonders why the gauges sold don't have an AN3 fitting to begin with.
One wonders why there are so many different fittings for the transmission of pressurized fluid.
Standards are wonderful, that's why there are so many different ones for the same purpose.
Firstly no USA company will pay any foreign company royalties period.
SOme will even refuse to pay royalties to USA based companies .
British companies refuse to buy new tooling so they keep on makng obsolete fittings .
The EU naturally want every thing to be metric.
And the Chinese want every thing to be made in China
Then things change over time so with all the high volume air tools around, the old quick couplers could not flow enough air .
Hydraulic pumps get higher pressure so the old couplings can not cope etc etc etc.