Additional tunnel for the Wall Entry Aluminum Pet Door™ (new model). Install your door in a wall more than 7¼ thick with this additional tunnel extension. The tunnel overlaps the pet door frame by 1 inch and fits walls 8¼ - 12 inches thick for the medium and large tunnel or 8¼ - 10¾ inches for the small tunnel. You can also cut the tunnel shorter if you need to install it in walls 7¼ - 8¼ thick. View door cut-out dimensions chart