Product Type: Sea Dog Stainless Steel Louvered Vent - Round - Model # SD-331424 - Diameter Edge to Edge: 4" - Diameter Vent Opening: 3 1/4" - Diameter From Mounting Hole To Mounting Hole: 3 5/8" - Vent Area: .88 square inches - Recommended Mounting Hardware: # 6 FastenersPart of the Sea Dog line of heavy duty marine hardware.Product Features:Stamped 304 stainless for lasting corrosion resistance.Instead of using toxic chemicals to get rid of mold and mildew, why not prevent it from showing up in the first place?Creating a steady flow of fresh air is one of the best things you can do onboard to keep your boat smelling fresh and mold-free.