90509-ZY3-000 Washer (7/8") - Overview. The 90509-ZY3-000 Washer (7/8") is a genuine Honda marine engine system part, designed primarily for use in fastening and spacing within various Honda marine equipment. This washer plays a critical role in ensuring the mechanical integrity and stability of assemblies where precise dimensions and reliable fastening are mandatory. Engineered for compatibility with Honda's factory standards, it ensures seamless integration with existing parts, maintaining opt