Thank you for all the replies.
My variac has only (female) banana plugs out and I wanted the adapter so I could connect bare wires up to it if I needed to w/o much fuss. I did come across that other style you linked to, Tiziano, that you need a screwdriver to adjust, but binding posts that have plastic insulated knobs would also be desirable, so those might not be best. The idea of frankenstein-ing 2 BNC adapters together did cross my mind, but I'm not too keen about that long thing hanging off my variac.
Considering the binding post --> BNC adapters aren't much different than what I'm looking for and are something like 99 cents each on aliexpress, I don't think I have unrealistic expectations to not pay $13 each, Tooki. As usual, I'll have to either wait until the Chinese copy it or just buy regular binding posts and solder a banana male to the backside of it.
Thanks again,