90303-ZW1-B03 Hex (16mm) Nut - Overview. The 90303-ZW1-B03 Hex (16mm) Nut is a critical fastener in Honda marine engine systems. This OEM hex nut provides secure and stable fastening for various components, especially within the water pump vertical shaft assembly and rigging systems of Honda's active marine product line. Designed to fit precisely within Honda marine engines, it ensures seamless integration with existing parts, maintaining optimal performance and durability.. Key Features. Hexago