Here’s a rare one! This ceramic cover is for 1920’s vintage Sphinx brand tub shower faucets. Sphinx was definitely an unusual maker, and some stems and still being made, but covers certainly are not. Hot/cold stems would have been on a 4″ center.
Cover measures 7″ wide by 5″ tall and extends from the wall 4 5/8″. No chips or flaws which isn’t bad for something that’s getting near the century mark.