The fuel cap is a small cap that covers the hole where you put the fuel into a vehicle. The fuel cap protects and covers the top of the pipe that connects to the fuel tank.
Usually made of plastic, fuel caps usually just clip or press into place over the opening. The fuel cap can be located on either side of the vehicle, towards the back, often on the quarter panel or rear wing.
The fuel cap serves to prevent dirt, dust and other unwanted debris from entering the fuel pipe and potentially clogging up and damaging the fuel filters. It also functions to stop fuel from spilling, leaking and evaporating out of the vehicle. The fuel cap also prevents others from accessing your fuel supply and siphoning the fuel.
Usual reasons for replacing this part is damage to or loss of the original fuel cap. Warped and badly fitting fuel caps won't function properly and will need to be replaced. Purchasing a fuel cap will ensure the part fits perfectly with the make and model of your vehicle.