Casio Ring Watch CRW001-1D Celebrating CASIO Watch’s 50th anniversary by bringing back the very first ring watch. With an inner diameter of 20 mm and a circumference of 62.8 mm, the ring fits a size 22 finger (US 10.5, EU U) and includes two size-adjusting spacers, in size 19 (19-mm inner diameter) and 16 (18-mm inner diameter). The rig features a 7-segment LCD that displays not only the time down to the second, but also the date, dual time, and stopwatch functionality.