Brought this brand new from BackCountry.com, and it's very easy to install.
I did feel safer using the longer screw came with the lock, than the original that came with the bike rack about 1/3 of the length compare to the lock screw.
The lock is very simple and very secure, all you have to do is tighten the screw thru the hitch with the rack, and put the lock on the other side and turn the key to lock it, that is all to it.
Even though the rack base is secure with this lock, but the rest of Thule rack can still be stolen. I don't know why Thule want to sell this lock to lock down the racks, but use the regular nut for the rest of the racks, that can easily be removed with the proper socket.
What I would like to see is Thule use those secure nut similar method that use on car wheel, that require a right key to remove.
Hope this help.