I am not sure but it looks like a 37. Someone has solderered it but it still works, and it has to be at least 85 yrs old. As you see I have a roarer burner too, but the ring is missing. Could not post a film, but I have some at Facebook under StoveAlcoholics posted january 27.
With the silent burner it's a 37! With the roarer it's a 31 With the mini silencer it's a 36 You wil find documentation at the library here at ccs