Help identifying regulator port size

[floridafrogman]

I need help identifying the thread size of an Italian manufactured regulator low pressure port. This is a 1980's vintage reg. called
"Spinnaker". It was made in Italy, for European distribution only,
therefore has metric threads. However, have not been able to identify the specific thread size/pitch. Any info would be appreciated. Conventional metric thread gauges don't work.
I assume this is a metric o-ring thread, similiar to our imperial 3/8" x 24 o-ring thread commonly used for American LP ports.

 

[Bob3]

I can't remember the size, the Cyklon had something like that way back when.
A 3/8" would just make it in for enough to strip things out & make a mess.
The Poseidon adaptors have "G 1/8 and 3/8 UNF" marked on them...
Gotta call the shop later on this aft, I'll ask.

 

[floridafrogman]

Bob3, appreciate your efforts. I tried an old Poseidon adapter, not the same! I beleive the older Poseidon's (which I owned) were considered metric but in reality they used a British thread
size/pitch that were a hybrid. Rick