Trapper, The small, square-headed, silver key with a 3 digit number stamped on it is part of the trailer hitch package. At least it was in my case. My trailer hitch wasn't on the car and was shipped separately in its own cardboard box. There was a sealed plastic bag attached to the hitch which had the 2 keys with the round red plastic heads and the third silver key. Not exactly sure what it unlocks but has something to do with the trailer hitch. Hope this helps a little.