90518-921-000 Washer, Plain (8mm) - Overview. The 90518-921-000 Washer, Plain (8mm) is a crucial component in Honda marine engine systems, serving as a flat, plain washer that ensures reliable mechanical assembly and load distribution. Its primary role is to prevent damage to surfaces by evenly distributing fastening force, thereby maintaining the integrity of connected parts. Carefully designed to factory specifications, this washer integrates seamlessly with existing hardware, preserving syste