90301-ZV7-000 Castle Nut - Overview. The 90301-ZV7-000 Castle Nut is an essential hardware component used in Honda marine engine systems, specifically designed for securing parts such as propeller shafts on Honda outboard motors including BF25 and BF30 series. This nut plays a critical role in locking the propeller in place, ensuring smooth and reliable engine operation. Crafted to meet precise factory measurements and tolerances, it ensures seamless integration with existing parts, maintaining