I was looking into replacing my portafilter spout and saw this online. Even though it's listed as 3/8" thread size, consumers are reporting that it doesn't fit their portafilter unless it's Breville. My question is, what is the thread size of Breville portafilter spout?
Thanks in advance.

Not quite an answer to your question, but the stock Gaggia Classic Pro portafilter seems to have a G 3/8-19 thread.

I saw some reviewers noting that it didn't fit Gaggia portafilter so I guess Breville's thread size is unique.