The screw plug K 43573 is an important threaded closure and sealing component of the automatic starting-air stop valve used in the starting-air system of the Adriadiesel/Jugoturbina/Zgoda/Sulzer ZV40/48 engine. Its primary function is to securely close a designated threaded opening in the valve casing, helping maintain the pressure integrity of the valve assembly and prevent unwanted leakage of compressed air during starting-system operation. Depending on the internal design of the valve, the screw plug may also provide access to internal components for assembly, inspection, or maintenance while ensuring reliable closure under normal operating conditions. Accurate thread dimensions, suitable material strength, correct seating geometry, and compatibility with the associated sealing elements are essential because damaged threads, improper tightening, or deterioration of sealing surfaces can lead to pressure losses, loosening, or reduced valve reliability. During service, the K 43573 screw plug is exposed to repeated compressed-air pressure cycles, vibration, temperature variations, and extended periods of operational readiness, requiring resistance to corrosion, mechanical deformation, and fatigue. During maintenance or overhaul, the screw plug should be inspected for thread damage, cracks, corrosion, deformation, worn seating surfaces, and signs of leakage, while installation should follow the manufacturer's specified tightening and sealing procedures. By providing secure threaded closure and maintaining effective pressure sealing, the K 43573 screw plug contributes to the integrity of the automatic starting-air stop valve, reduced compressed-air losses, dependable starting-air control, and reliable long-term operation of the ZV40/48 engine.