I'm giving the lock one star because the prop fell off when I started the boat. Luckily I found the prop. My son went into the water and found the prop. I followed the directions correctly and verified installation with McGard. When I spoke with Mcgard they said I installed the lock correctly. I asked them why the prop fell off. He asked me if I used never seize on the threads. I said no. I did use the special grease that the mercrusier manual said to put onto the threads on the shaft. He said you can't put grease on the threads thats what made the lock fail and the prop spin off. Not so sure I accept this answer, especially when the manual calls for greasing the shaft. I took the lock off and kept the grease on the threads and went back to using the tab washer and nut on the prop. I'll take my chances without the lock.