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 unique back-up sealing wall leaves the plate water resistant, even if the gasket is removed. A screw-out plate should be used in compartments where a change in air pressure due to temperature or oil canning can occur. These deck plates seal by easily aligning the notches and twisting the top to tighten. O-ring seal Watertight Lightweight Non-corroding Durable