The Beckson Screw-Out Plate was designed to provide access without the use of tools, with a single start non-jamming (no cross-thread), extra strong, self-cleaning buttress thread. They incorporate a self-aligning center and an innovative gasket to assure a watertight seal. A patented 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, inspectionk 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. Outside diameter trim ring measures 6-1/8": Hole cut 4-1/2": Passage 4".