Cowl VentilatorAttwood 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″WARNING: This product can expose you to chemicals which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.