McGard Propeller Lock For OMC, Mercruiser, Mercury, Johnson & Evinrude Protect yourself against expensive propeller theft with a McGard propeller lock, featuring the same patented design as our stern drive and outboard motor locks. A free-spinning collar will turn if attacked by gripping tools without loosening the lock. Constructed of naval brass and hardened stainless steel, once installed our propeller lock offers maximum security for 24 hour protection. 3/4-16 Thread Sterndrive Engines MerCruiser Alpha I, Bravo I Stainless Steel (Incl. X & XR), TRS, Vazer; OMC Cobra and King Cobra; Outboard Engines Mercury/Mariner 70 HP and larger (ex.225 HP 4 stroke before 2005); Mercury Bigfoot 40 HP, 50 HP, 60 HP (4 stroke); Optimax 75 HP and larger; Verado 135 HP and larger; Johnson/Evinrude 150 HP and larger (2 stroke);