90503-ZW4-H01 Washer (10mm) - Overview. The 90503-ZW4-H01 Washer (10mm) is a genuine Honda marine engine part designed to support the mechanical and rigging systems of Honda Marine equipment. This washer plays a critical role in distributing load evenly across fasteners and preventing damage to connected components, thereby maintaining system integrity and reliable operation. Manufactured to strict OEM specifications, it ensures seamless integration with existing parts, maintaining optimal perfo