Perko - Cowl Ventilator - Chrome Plated Zinc Alloy - 3" - 0870DP0CHR. Chrome Plated Zinc Alloy Cowl with Black PERKO-KOTE Base. 3" Duct Thread into Neck, Hose Clamps Not Required. Cowl Opening - 7-1/3 square inches. Length - 5-1/8". Width - 4". Height - 3-7/8". Screw Size - #10