90559-ZW1-000 Washer Plain (12mm) - Overview. The 90559-ZW1-000 Washer Plain (12mm) is a crucial component designed to support the hardware system in Honda marine engine systems. This plain washer provides a bearing surface and evenly distributes the load under fasteners to maintain secure assembly and structural integrity, ensuring the marine engine operates reliably. Manufactured to meet strict factory specifications, this washer seamlessly integrates with existing parts, maintaining optimal p