This white Hayden Exhaust Vent Cap mounts on the outside of your house where the central vacuum exhausts the air. It has a 2 1/2" square flap which blows open when the vacuum runs and closes automatically when not running. Two screw holes on 3 5/8" centers enable you to secure it to the wall.
The dimentions of the faceplate are 3 5/8" wide and 4 5/8" high. If has a female opening on its back which mates with the standard "Schedule L" thin wall PVC pipe.