90506-ZV4-000 Plain (6mm) Washer - Overview. The 90506-ZV4-000 Plain (6mm) Washer is a critical hardware component within the Honda marine engine systems. This washer is designed to serve as a general-purpose fastener support, ensuring secure mounting and reliable performance under a variety of operating conditions. Its primary role is to distribute load and prevent damage to surfaces in contact with bolts or nuts, maintaining the mechanical integrity of assemblies throughout the marine engine s