90511-ZW9-000 Plain (9Mm) Washer - Overview. The 90511-ZW9-000 Plain (9Mm) Washer is a crucial component in Honda marine engine systems, serving a fundamental role in securing fasteners and distributing load evenly. This flat metal ring, measuring 9mm in diameter, supports assemblies that rely on maintaining pressure and spacing between parts, reducing wear and enhancing mechanical reliability. It ensures seamless integration with existing parts, maintaining optimal performance and durability..