Perko s 1312DP0CHR Cowl Ventilator is constructed of chrome plated zinc alloy and features a black polymer base. It has 3 ducts that thread into the neck and hose clamps are not required. The cowl opening is 8 square inches and the dimensions of the cowl are 5-3/4 L x 4-3/8 W x 2-5/8 H. The required screw size for installation is #8.