The lock washer, code 100100, is an important fastening and securing component used in the MAN L21/31 engine to help maintain the integrity of bolted or threaded connections under demanding operating conditions. Its primary purpose is to reduce the risk of unintended loosening caused by engine vibration, cyclic mechanical loading, temperature variations, and repeated operational stresses. Depending on the particular fastening arrangement, the lock washer provides an additional securing effect between the fastener and the adjoining surface, helping preserve the required clamping force and stability of the connection. Correct dimensions, suitable material properties, proper surface condition, and installation in accordance with the specified assembly procedure are essential for reliable performance. During maintenance, the washer should be inspected for deformation, cracking, corrosion, excessive wear, or loss of its locking capability before reuse. By helping prevent fastener loosening and maintaining secure mechanical connections, the lock washer contributes to operational safety, reduced maintenance risk, and the long-term reliability of the MAN L21/31 engine.