WWII AAF A-13 Oxygen regulator.
Portable Warbird Oxygen Diluter Demand Regulator. Manufactured by Scott Aviation Corp.
Type A-13. The data plate confirms the maker, type and contract number. It has a clip on it that attaches to aircrew uniform when used, and the instrument and bezel are still attached with a Perspex glazing unit.
Used on various walk round Oxygen bottles issued to AAF Aircrew
This particular unit has some issues. The clothing clip is slightly bent and the bezel and Perspex is missing from the instrument. The hose clip cover also needs some attention.
Having said the issues can be rectified and A-13 demand regulators rarely seem to come to the market these days
The last photo shows the type of Oxygen bottle that this unit would have been fitted to