This is a high quality waterproof inspection Deck plate made of UV stabilized plastic. Opening Diameter: 4" Overall Diameter: 5.8" Distance between two opposite screw holes: 5" You will need to use silicone waterproof sealants on each of the six screw holes to prevent water from seeping through the holes. The recommended screws for this deck plate is P20004-01. Item: P13560BK