90310-ZV5-821 Hex (4Mm) Nut - Overview. The 90310-ZV5-821 Hex (4Mm) Nut is an essential component used within Honda marine engine systems. This hex nut plays a critical role in securing assembly parts, contributing to the reliable and efficient operation of Honda marine engines. With a precise 4mm dimension, it ensures seamless integration with existing parts, maintaining optimal performance and durability.. Key Features. Genuine OEM Honda hex nut designed specifically for marine engine applicat