1-5/16" with a fixed loop and moveable ring on top edge. Each side has beautiful color graphics related to the Buffalo 1901 Exposition. The piece opens and holds pair of printed black and white photos of two different Exposition buildings. There is one circular piece of celluloid which once covered one of these but which has apparently shrunken with time so it is not quite large enough to stay in position. The exterior front and back celluloid are NM displaying Mint. While we've seen both of these celluloids as individual pin-back buttons we've never seen them combined to form a locket.