Designed for Yamaha lower units, we feature a SS locking bolt. Simply replace one of the original bolts above the propeller with a McGard locking bolt. Once installed, the lower unit lock bolt offers 24 hour protection. Constructed of through-hardened stainless for maximum security. A free-spinning collar will turn if attacked by gripping tools without loosening the lock. For maximum security, use in conjunction with a Yamaha lower unit lock bolt.