Breathing on the top of the 1934 fuel tank?

Posted by Odd Moen On 2018/7/15 14:54:33

On the top of the 1934 fuel tank it is small welded construction with a diameter app 2``and height app 1``1/2.
Is ithis a float or a valve,?
I want to manufacture a new fuel tank, and therefore I`m wondering about how this item operate.