90309-ZV5-821 Hex (5Mm) Nut - Overview. The 90309-ZV5-821 Hex (5Mm) Nut is a critical component used in Honda marine engine systems, specifically supporting rigging and accessory assemblies. This hex nut with a 5mm inner diameter plays an essential role in securely fastening parts and maintaining the integrity of the marine rigging system. Engineered to exact Honda factory specifications, it ensures seamless integration with existing parts, maintaining optimal performance and durability.. Key Fe