I could not lock the pin until I ground off about 1/8" of metal on each side of the receiver around the hole, tapering it to match the shoulders of the lock.  Chevy and GMC HD 2500/3500 pickups put on an honest Class V hitch that is a full 3 1/2 across, and in spite of the claim, this product is just a bit short.  Regardless of the needed modification this is a quality lock that should deter even an ambitious thief!  I would not recommend grinding on the lock as that might weaken it.