I want to make a temporary pressure gauge for my Gaggia Classic but am really struggling to figure out which adapter and pressure gauge I need

What thread size/type is the portafilter on the Gaggia Classic?

Is a pressure gauge with a snubber necessary? Anyone mind sharing which gauge you purchased?

I wrenched off the spouts and took the portafilter to my local hardware store. A guy there found me a pressure gauge (not anything special) and the necessary fittings. I wrenched it together and it was easy and cheap. He barely spoke English but we figured it out.

That's what I'm hoping. I don't want to spend $50 on something I'm going to use for 10 min every 2 or 3 years.

I belive the threads are probably 3/8" BSPP (can't seem to confirm this though), so I was a bit worried about running a pressure measurement with the wrong threads (3/8" NPT). Maybe some extra teflon tape will resolve the problem well enough for the test...

Was it just a generic, low cost air filled gauge and, if so, did you have any trouble reading the dial like some people have claimed?

I also see conflicting reports on the no flow vs flow testing conditions. Many say just attach a closed off pressure gauge and subtract 1 bar to account for flow, but others claim that can yeild wildly unrealistic results and say you need a needle valve to simulate a shot. Thoughts?