These washers are made to thread directly into the face of the CGA 320 CO2 valve.  These washers remain on the cylinder.  There is no need for a washer inside the regulator nut.  It also makes filling cylinders quicker.  There are no dropped washers.  The O-ring allows for easy sealing. The user does not lose the washer. The part number for this item is ACM-327.

Aircare Medical Supply also has a variety of other washers and seals for both post valves and the larger valves. The most popular CO2 sealing washer is the yellow 750 medical washer; part number ACM-033 and the green 750 medical washer, part number ACM-001.  These seals are for the CGA 320, larger, valve.  For post valves, use washer part number ACM-017, or ACM-002.