I have to assume that there is a standard. I just don't know what it is.
This is the old R-12 fitting.

Thanks.

Edit - Google search says 3/8". Is that correct?

[This message has been edited by Raydar (edited 09-04-2014).]

3/16" (3/8"-24 thread)

Looking for an R-12 hose adapter (Mastercool 90355), or an R-134A conversion fitting (4 Seasons 59978)? Replacement Schrader valve is GM part # 10027604, or AC Delco part # 15-5375 if you're keeping it R-12, will need a special tool to replace it like Four Seasons 59302

[This message has been edited by RWDPLZ (edited 09-04-2014).]