That would open up the use of several differing rubber mouldings as this is standard pipe section.
The Trienkel used a sort of silver plastic material for at least part of the production run. The material is also found being used to make the hubcaps and prettily badged oil grommet on later chain-cases with the Bakelite type cover plate. These were intended to be fitted warm when the material is pliable as it is pretty rigid at normal room temperature. I have several old ones but they tend to discolour. In the Trienkels case it unusually has the fuel tank inside the main body of the car. The seal thus needs to be water tight or the bottom of the tank resting on soft material rusts out with the body floor below. Since this sits above the engine a nice hot steamy bath of water each run out is just the job for naff node major. Pin hole leaks on Trienkel tanks are a well known problem, and this is why. In most instances the tank neck grommet does not need to be 100% water tight as it is not entering the body and/or has a drain trap to collect spilt fluids and void them neatly, not so the Trienkel. This is why the Treinkel tank and grommet are a tricky thing to fit correctly. Not only has the grommet to be inserted with the flange in place and the neck through, a stern battle, but then the whole thing needs to be centred. Despite the body having a slot for the fuel tap thread to poke through into the engine bay you will be surprised how often it is a struggle to get good alignment, especially if the car is a restored one and accuracy has been lost. In my experience most restorers do not bother to mount the grommet correctly and pass the problem on.
