These pieces (3 shown) predate 1990. I don't know which set they belong to or what they were/can be used for. I asked Lego but they didn't know either.
This is most likely Scala Jewelry Plate, Modified 2 x 2 (Human Bracelet segment).
Quite easy for me to find on Bricklink's search engine. All I did was type "plate 2x2 modified." Bricklink tells it appears in four sets which look like bracelet kits, but as of now it's too late to use them as bracelets because Lego has already invented newer ones. You might as well use these as a bridge or something.