Beckson Marine 4" Smooth Center Screw-Out Deck Plate - Black. They incorporate a self-aligning center and an innovative gasket to assure a watertight seal. A back-up sealing wall leaves the plate watertight even if the gasket is removed. Deck plates are used for access to shut-off valves or back-fastenings inspection and clean out for tanks and compartments. A screw-out plate should be used in compartments where a change in air pressure due to temperature or oil canning can occur. Center: Smooth Color: Beige Package Contents: Beckson Marine 4" Smooth Center Screw-Out Deck Plate Beckson Marine DP40-B: 4" Smooth Center Screw-Out Deck Plate - Black