The material for nuts, code 300100, defines the engineering material requirements for fastening nuts used in the MAN L21/31 engine, where reliable bolted connections are essential for maintaining structural integrity under demanding operating conditions. Materials selected for these nuts must provide appropriate mechanical strength, toughness, dimensional stability, and resistance to cyclic loading, vibration, elevated temperatures, and the operating environment encountered in marine and industrial service. Depending on the particular fastening application, correct material properties are especially important for maintaining the specified preload and preventing deformation, excessive wear, corrosion, loosening, or premature failure of the connection. Compliance with the prescribed material specification, together with correct machining, heat treatment where required, and proper tightening procedures, contributes to dependable fastening performance, safe engine operation, reduced maintenance requirements, and the long-term reliability of the MAN L21/31 engine.