C-H,
I can't say that I've ever liked the Pg sizing system, for cable glands and so forth.
I've always found the Metric threading sizes a lot easier to use, but that's only my personal view!. [Linked Image]
Oddly enough, (and I really hate to play the EU card here) there is (like for other things) an EU Directive on Cable Glands and the like, it's called prEN 50262, but I have a feeling it may apply to more than just Cable Glands.
I didn't dare do a web search on it, for fear of getting lost in the technical data!. [Linked Image]