The fuel filler hose passes through the cabin area of the car. Therefore it needs to be enclosed to keep vapors etc. out of the cabin area. This is done with a hose over the outside of the filler hose that’s seals of the cabin from the fuel tank – hose space, the hose used:
Which came from HERE.
The fuel filler screws from the outside go through into threaded holes in an aluminium ring, on the inside the same ring has the flange for the outer hose screwed to it from the other direction. The outer hose then clamps onto the flange at either end.