Clear float bowl plugs
From my experience with the plastic (clear acrylic) is that tend to dry out and break in half right at the threads.
Then you have the threads stuck in the bowl and nothing left to grab onto to get them out. You end up having to take the bowl off and drill a hole in the threaded to remove them.
So I learned to just use them when setting the float levels and then put the metal plugs back in.
Tom