The best protection available against costly propeller theft. Once installed the McGard propeller lock offers 24 hour protection during use, storage and transit. A free-spinning collar will turn if attacked by gripping tools without loosening the lock. Constructed of naval brass and hardened stainless steel for maximum security. Fits the following stern drives: MerCruiser III SSM, IV SSM, V SSM, VI SSM. This product may contain globally sourced materials/components.