Model No.:ZB1701-4 Speficication of air vent cover The surface is polished . Good material and excellent polishing quality make it has good performance on anti-rust and corrosion resistance . This air vent cover is produced in stainless steel material , which is solid and durable 2 sizes are available for you 4 inch and 5 inch. Stainless steel 316 5' inch marine round louvered vent for boat yacht 5 Round Louvered Air Vent Easy to use and install. 316 stainless steel, corrosion resistance and durable. Great for related vents in boats, marine, yacht, caravan, home