Tis backing plate is commonly found on 1940’s through mid 1950’s 6″ center shelfback lavatory faucets made by American Standard. The original ones were made of Zinc, and they tend to corrode. These replacement parts are Chrome plated solid Brass. They measure 1 3/4″ on the outside, and are 13/16″ on the inside. They thread directly onto the original Standard valve body. Sold by the each.