Attwood Louvered Vent OffWhite #2314951Constructed of corrosionresistant ABS plastic with no sharp edges. For 3" I.D. ventilation system with 1345 collector box. Install with #8 screws. Attwood hullmounted vents are designed to install by fastening as a complete unit from either inside or outside the hull.Hole Size, 21/4'' H x 16'' L