Most of my experience with USD manifolds has been with older vintage sets that for some strange reason used the standard Oxygen connections, CGA-540. At some point in time they changed to the standard and more appropriate Air connections, CGA-346.
I'm not sure when that occurred, and only noticed a couple of years ago that i had some of each. Anyone know when that change took place?
Newer valve on the left is CGA-346 connection, the compressed gas industry standard for AIR.