I have the Colonial 23, the shelves have a plastic guard in the front, 1 inch thick and I bought the over/under pack.
With effort the hangers slide on all the way, but they are not secure(move side to side with no effort).
If I take off the plastic guard they fit well, but it's not carpeted under the guard and I don't want an unfinished look.
So if you're like me and have the plastic guard in the front of your shelves I'd look at the back over/back under hangers instead, unless you're fine with an unfinished looking safe or plan to re-carpet the shelves.