90508-ZW1-B00 Washer (18.5Mm) - Overview. The 90508-ZW1-B00 Washer (18.5MM) is a critical component within Honda marine engine systems, specifically designed for use in propeller shaft assemblies and related marine applications. This plain washer plays a vital role in supporting proper assembly and maintaining mechanical integrity, ensuring optimal operation and durability in demanding marine environments.. Key Features. Plain Washer with 18.5MM diameter, precision manufactured.. Genuine OEM Hon