The locking spring washer, code 515151, is a critical fastening component used in the MAN L21/31 engine to prevent loosening of bolted connections caused by vibration, thermal cycling, and dynamic mechanical loads. Designed with spring characteristics that maintain continuous preload in the joint, it enhances the security and stability of assembled components during prolonged engine operation. Manufactured from hardened, wear-resistant materials and protected against corrosion, the washer delivers dependable performance in severe marine and industrial environments. By maintaining fastening integrity and reducing the risk of connection failure, the locking spring washer contributes to operational safety, lower maintenance requirements, and the long-term durability of engine assemblies.