Canted louvers deflect rain and spray and help conceal the collector box. Installs flush to hull. Drain slots to prevent water accumulation. Black vent is ABS plastic, white vent is ASA plastic. Install with #8 screws. Requires 1341 collector box for 3" system, or 1342 for 4" system. Attwood hull-mounted vents are designed to install by fastening as a complete unit from either inside or outside the hull.