Although the 'butterfly' is plated brass, the rest is steel.
Tatty / incomplete examples are not that difficult to find and they can usually be restored. Early-war were dull-chrome plated, later cadmium.
They are a larger version of the oil tank cap and bear the 'Enots' ('Stone' from Benton & Stone backwards) trademark on the internal closing mechanism.
Some brass caps do exist, I have an original larger version on my M20 petrol tank, and I made an oil tank cap to match which is the same size as the 16H fuel tank cap.
The original is probably local manufacture from India or the Middle East and I don't know for sure that its wartime, but I do like brass so I'm happy with mine.
Does anyone else have an original of any of the 3 sizes?
