90501-ZY1-000 Plain Washer - Overview. The 90501-ZY1-000 Plain Washer is a fundamental flat metal ring designed for use within Honda marine engine systems. This part supports secure fastening by distributing the pressure of bolts or screws evenly across surfaces, preventing damage and ensuring a dependable mechanical assembly. Widely utilized in power trim-tilt mechanisms and other rigging assemblies, it ensures seamless integration with existing parts, maintaining optimal performance and durabi