How does it work? Easy Fill

So there are little spring-loaded tabs around the opening. Press those tabs in (towards the outside perimeter of the ring), and it "unlocks" the door to the fuel tank. The size of the opening is small enough so that as long as you are using a standard gasoline pump nozzle, it will always depress the tabs and therefore always unlock the door. The little insert thing they provide you is just wide enough to depress those same tabs the pump nozzle presses.

Hopefully that made sense?? Kind of a hard thing to describe. Pitch black outside right now but perhaps tomorrow I'll film a video with my phone. You can open the fuel door with a carefully placed stick in case you are an idiot like me and lose your little white plastic insert.