1-3/8" dia. with .5" stud back. Outer edge tappers inward and the piece is about 3/16" thick. There is a tiny hairline crack at the very bottom through the beveled edge of the tortoise shell but not through the mother of pearl inlaid accent beneath the word "Philadelphia." This hairline barely shows and the rest of the piece is quite spectacular for an 1876 item with the mother of pearl giving off soft blue and pink reflective colors. We once saw a somewhat smaller similar set designed as cuff links but given the larger size of this piece we think it was meant for a suit jacket buttonhole. See Palmer Cox Brownie spoon for 1893 expo #1514.