Two of my lenses are 21-1/4. I bought the second for the mounting ring and flange. They were meant to be mounted with a 90 degree prism that reverses the lettering on the front. With the prism it says, "Kodak Copying Ektanon". With the prism removed it says, "nonatkE gniypoC kadoK". The third is a 10 inch. All are dated ES or '47.