Cowl Ventilator Attwood hull-mounted vents are designed to install by fastening as a complete unit from either inside or outside the hull. Ventilation hose not included twists into the bottom of the box to form a raised water barrier. Plastic vents are corrosion-resistant, will not discolor. All collector boxes and vents are designed for intake or exhaust and meet ABYC H-2 cross sectional area requirements. For use with 3 I.D. wire-supported ventilation hose. Features flexible hose flange that is screwed onto hose, then vent snaps onto the flange. Vent constructed of chrome-plated die-cast Perma-Plate ZAMAK. Flange is non-corrosive plastic. Installs with #8 screws. Installation Hole Size 3-1/4 to 3-1/2 Attwood Cowl Ventilator 1364A3