Attwood Cowl Ventilator 6" 

"Can be used with any standard 3" ventilation hose. Features flexible hose flange that is screwed onto hose, then snaps onto the flange. The neck extends 1" below deck. Chrome-plated zinc. Flange is non corrosive plastic. Installs with #8 fasteners. "

Size: 6" L x 5-5/16" W x 2-1/4" H", Hole: 3-1/4" to 3-1/2" dia.", Case: 6

Sold: Each