The locking spring washer, code 515151, is a critical fastening element within the MAN L21/31 engine, specifically designed to prevent loosening of bolted connections caused by vibration, thermal cycling, and dynamic mechanical loads. Featuring spring characteristics that maintain continuous preload within the joint, this washer enhances the security and reliability of assembled components during prolonged engine operation. Manufactured from hardened and wear-resistant materials with additional corrosion protection, it provides dependable performance in severe marine and industrial environments. By ensuring fastening integrity and maintaining stable mechanical connections, the locking spring washer contributes significantly to operational safety, reduced maintenance requirements, and the long-term durability of engine assemblies.