The black plastic fuel filler adaptor is for emergency use, if you are having to use a jerry can or similar to add fuel. It defeats the easyfuel system built into the neck of the fuel pipe, which normally only lets the correct sized fuel nozzle to be used when filling the tank. This feature avoids mis-fueling! There are anti theft devices built into the filler further down the neck. So, keep the adaptor in the car, you won't need to use it unless you run out of fuel!