Bruce L. Bergman writes:

But not an adapter ...

The EPA holds that if certain fittings are required, then adapters to
circumvent them are not permitted, since that defeats the very purpose of
the fittings, namely to make impossible the mixing or confusing of
refrigerants. While the utility of adapters is obvious, you're supposed to
have a separate set of gages and hoses for each refrigerant. That's the
governmental logic: intelligent economizing must give way to backstopping
presumed stupidity.

As Uncle Al sez, environmentalism is expensive, shoddy, and deadly.