RAF aircrew oxygen mask hose connectors, types Mk IV and IVa.
Air Ministry stamped with reference numbers. Bayonet fitting Mk IV, Ref No. 6D/526 is new old stock and complete with a crocodile clip. The top bayonet receptacle brass fitting is for the walk around oxygen bottle extension hose, Ref No. 6D/482.
Both items are in excellent condition.
NOT FOR SALE to the EU.