The washer, code 100100, is an important mechanical fastening component used in the MAN L21/31 medium-speed diesel engine to distribute clamping forces evenly and provide a stable bearing surface beneath a bolt head, nut, or other fastening element. Depending on its specific installation position, the washer helps protect adjoining component surfaces against localized deformation, indentation, and wear while supporting the correct preload and mechanical stability of the bolted connection. During engine operation, fastening assemblies are exposed to continuous vibration, cyclic mechanical loads, temperature variations, and demanding operating conditions, making washer dimensions, material strength, hardness, surface finish, and proper installation particularly important. Correct selection and positioning of the washer are essential to prevent uneven load distribution, loosening, and premature deterioration of connected components. During maintenance and overhaul, the washer should be inspected for deformation, cracking, corrosion, excessive wear, damaged contact surfaces, and other signs of deterioration before reuse. By maintaining effective load distribution and supporting secure mechanical connections, the washer contributes to structural stability, reduced fastening-related failures, operational safety, and the long-term reliability of the MAN L21/31 engine.