Fits flush to boats transom or exterior, allowing water to drain when boat is trailered to prevent moisture build-up and rot damage. Celcon pipe plug has screwdriver slot. Natural color nylon tube won't bend, rot, or mildew. Three recessed holes allow riveting into transom, or can be secured with #8 fasteners. Rubber O-ring makes the unit water tight. Tube & Plug with "O" ring.