The quarter panel is the portion of an automobile's body which corresponds to the fenders in front. It encloses the area around the wheel (in conjunction with the wheel house) and provides the outer skin on the rear of the sides of the car. On most passenger cars the fuel fill is in a door on one of the quarter panels, and there is frequently a side marker light near the rear of the panel. Quarter panels began to replace rear fenders in the 1930s with the advent of unibody designs from Volkswagen and Nash. They are welded to the body of the car and must be cut away to be replaced, though they are often repaired instead. The upper portion of the quarter panel where it runs up toward the roof behind the side windows is known as the sail panel or sail area due to its upright triangular shape.