The lock is designed to secure the lower unit to the mid-section of the outboard while in storage, on the trailer, or in use. A free-spinning collar turns if attacked by gripping tools, helping protect against costly lower unit theft. Simply replace one of the standard lower unit mounting bolts with a McGard lower unit locking bolt. Use the included special key to remove the McGard lower unit locking bolt when removal of the lower unit is required. Stainless steel, through hardened construction. Fits Yamaha outboards F115 – F350 without 5” extension.