This aerodynamic cover prevents odours from entering the RV by creating a vacuum while the vehicle is moving. Low, smooth profile keeps branches and tree limbs from catching and causing damage to the shroud and vent pipe. Inside it has a bu"ilt in aluminum screen to keep unwanted pests out. Fits vent pipes up to 3 inches. Installs in minutes. Outer dimension: 7 1/2" x 6 1/4" x 2 1/4" Inner dimension: 5 1/4" x 4 3/4"