1.25". Reverse has Bastian paper first used 1907 and button is from that era. Paper has some margin stains and a missing sliver. The collet has some minor oxidation. The only marks on the celluloid are three exceedingly faint gray spots each about 1/16" or smaller along the most extreme upper right rim edge. These show very little and about 97% of the celluloid area remains Mint. Superb coloration. Full gloss. A rare button we've seen perhaps only twice before.