I do not know the details of how the float is retained on a ‘31 flue gauge sending unit.

What I do know is that I regret installing a new cork float on my ‘37 sending unit. After less than 3 months it had absorbed enough gasoline that it did not register correctly. It still worked but indicated at least 1/4 tank lower than actual. I think it is even further off now.

So now I need to adapt either a neoprene or brass float.