90501-ZW4-H01 Washer (5mm) - Overview. The 90501-ZW4-H01 Washer (5mm) is a genuine Honda part designed specifically for use in Honda marine engine systems. This washer provides critical support within mechanical assemblies, ensuring secure fastening and proper spacing in various components. As a small yet vital element, it contributes to the overall reliability and durability of your marine engine by maintaining stable connections under operational stresses.. Key Features. Genuine OEM Honda wash