NSN 4820-01-538-6589

A metallic, threaded, screw-shaped item used in hydraulic brake cylinders, hydraulic power units, missile launching hydraulic systems, and the like, for the purpose of providing a means of releasing air form and/or flushing a hydraulic system. It may be furnished with or without a dust cap. Excludes spring loaded or automatic type air pressure relief valves, and bolt, fluid passage.