Made of Marine Grade 304 Polished Stainless Steel for maximum corrosion resistance and durability Commonly used for Marine Companionway Door, Cockpit, Cabin Ventilation, or use for household shed or additions Easy to install and maintain, without modification and it is not easy to fall off. Repairs can be completed in a short time and hardly require any mechanical expertise. Commonly used for Marine Companionway Door, Cockpit, Cabin Ventilation, or use for household shed or additions Dimensions: Thickness: 1mm 0.03" (0.8mm ); Diameter: 4"(100mm) Package Includes: 1 pc of MARINE CITY Stainless Steel 4" Round Butterfly Vent with Center Knob Shutter Vent.