90303-ZW5-000 Hex (18mm) Nut - Overview. The 90303-ZW5-000 Hex (18mm) Nut is a critical fastener component designed for Honda marine engine systems. This hex nut plays a vital role in securing various assemblies within the marine rigging and accessory systems to maintain reliable engine operation. Manufactured to meet Honda's exacting factory specifications, it ensures seamless integration with existing parts, maintaining optimal performance and durability.. Key Features. This is a genuine OEM H