Constructed of corrosion-resistant ABS plastic with no sharp edges. For 3" I.D. ventilation system with 1345 collector box. Install with #8 screws. Attwood hull-mounted vents are designed to install by fastening as a complete unit from either inside or outside the hull. Measures: 3 7/16"W x 17 7/8"L x 3/4"H (thick) Cut Out Dimension: 16" x 2 1/4". Proper ventilation keeping fresh air flowing through passenger areas as well as the bilge, engine and fuel tank area is not only important for passenger comfort, it's essential for boating safety. Meet the need for safe on-board ventilation with Attwood, the leader in marine ventilation.