The ventilator is secured with a locking washer against closure when mounted in a caravan. If you mount it in a boat, or where closure is allowed, you can easily remove the security washer with a screwdriver. Complete ventilator with nylon or stainless steel cover. Lockable in closed position. Adjustable for deck or roof between 3-40 mm (1/8-1 5/8). Screws included.