License plate question

So we took the license plates off of my wife's B so that we could get the new personalized plates. When I got back from DMV, I went to put the new plate on the back and apparently there should be something that it screws in to. The screws just spin on the license plate frame and I can push them in by hand. What am I missing and is it something I can get someplace simple, like a hardware store?

Thanks,

well normally one uses the special licence plate plastic self locking nuts and screws sold by any Auto supply store or probably your local supermarket that has a auto section