filler cap 
noun
A cap closing the pipe leading to the petrol tank of a motor vehicle.On the outside, all it lacks is a pair of running boards - chrome is again used to stunning effect on the wheels, door handles, filler cap and exhaust tail pipe, while bumpers and side mouldings are body-coloured....
- The petrol filler cap was smashed on arrival, so I've emailed the vendor to see if a replacement can be provided.
- Inside the boot is the lever for opening the fuel filler cap.