This knee buckle, used to fasten the bottom of knee breeches just below the knee, was worn by George Washington on the day of his inaguration, 04/30/1789. It is made of brass, paste rhinestone, mother of pearl, and measures about 1.25″. For source and more details, click here.
Image from: http://www.cr.nps.gov/museum/exhibits/revwar/image_gal/morrimg/kneebuckle.html