RAF oxygen mask bayonet union.
Air Ministry stores reference number 6D/112, sockets Mk IIIB.
This brass oxygen bayonet accepts the hose connector fitting 6D/101 (see last photo).
The fitting was used with the type D oxygen mask and hose.
Air Ministry stamped on the base, and dated 1939 on the side.
In an excellent condition.
NOT FOR SALE to the EU.