A Gas Cap is used to seal the gas tank in any vehicle. The main purpose of the gas cap is to ensure that the gas tank is air tight. This not only keeps the dust and dirt out, it also helps to ensure that fuel does not come into contact with the atmosphere. A gas cap is made using heavy duty plastic material for most vehicles. So it can easily seal that dirt out, and the fuel inside the tank. This gas cap can easily be fitted and removed from the tank, when need be. The gas cap is like a bottle cap, and can be completely removed to fill in the gas, and then capped back on when the fuel has been filled. The gas cap comes in one standard colour for most vehicles, as it is going to be hidden under the small door, there is no need for it to be flashy or anything. The gas cap only serves one purpose that is to seal the tank.