The locking spring washer, code 515151, is a critical fastening element 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 tension within the joint, it enhances the security and reliability of assembled components during prolonged operation. Manufactured from hardened, wear-resistant materials and treated for corrosion protection, the washer provides dependable performance in harsh marine and industrial environments. By helping maintain proper preload and fastening integrity, the locking spring washer plays an essential role in operational safety, reduced maintenance requirements, and the long-term durability of engine assemblies.