This is the DeVilbiss Caire Quick-Disconnect Coupler Fitting CAIRE 10666439 QDV 15/16" NPT. This is the stainless steel QVD coupling case only, and not the whole assembly.  It is part of the Pulsar / Devilbiss 10577858 (or 1062014-001) Caire QVD Gen II Female Assembly.