I can't imagine it would be anything other than 1/4" NPT unless it was
3/8" NPT. Gotta be one or the other.

wow, guess we found a big hole in my tool knowledge. what is this?
does it describe the thread pitch or something? Is it the same
threading that the borg will put on black pipe for you, like for pipe
clamps?

Don't get too excited about that 6HP unless you bought an
Ingersoll-Rand.

It's porter cable which is certainly made by someone else. I heard
that devilbiss made their compressors for them. I'd be surprised if it
wasn't chinese.

I've seen 6hp "running" and 7.5hp "peek" whatever that means. I found
the manual online after I posted. It says 30 amps though so the 6hp
number is probably close to reality.

brian