Oxygen Flow Indicator, MK II, British Royal Air Force, 1942
Here is a WW2-era artifact: an Oxygen Flow Indicator, Mk II, Stores Reference 106D/26, made by Westinghouse. Multi-crew RAF aircraft had these installed at crew stations, such as gun turrets, radio operator, navigator, etc., to indicate the gross flow (not the precise rate) of oxygen from the primary oxygen tanks (not portables) to the local junction at each station. Commonly used in aircraft such as the Lancaster, Wellington, Stirling, Mosquito, etc..
This is New Old Stock in its original box dated 1942, and the ports are capped. Measures ~2 inches diameter and 4 inches port to port.