Thats true when I ordered mine, it was a listed part number. After getting the hitch and spreading the lower bar, I called and ordered the adapter. It was back ordered. and then I got a card saying that the supplier wasn't going to be able to supply the adapters anymore.
So I sent mine back. Now I see they are offering them . Don't figure.But it does to some extent considering HF.
Id order both together. I would think that good marketing would dictate that they were both advertised together. Your right on the shipping. The more stuff the merrier.
Good luck
Allan