Jcrow- What do you mean your machine won't recognize it? I don't think my machine has any way of knowing what foot is on it, so it doesn't make a difference.
Do you have one of those fancy machines that needs coded feet? Is there just not a coded #20?
Thanks all for the advice. My trip to the store (it is an hour away) got postponed and I made due with my number 23. I don't love it, but I have a beautiful stack of Dresden Plate blocks, so it all worked out!