1-3/4" Triple Ring: The largest of the three rings on this size is 1.75", and that is the ring which is designed to encircle both the cock and balls. The second largest ring is 1.5", and goes around just the cock. The smaller ring is 1.25", and is just for the balls. If you normally wear a 1.75" diameter cock ring (or slightly smaller), this would be your size.
2" Triple Ring: The largest of the three rings on this size is 2", and that is the ring which is designed to encircle both the cock and balls. The second largest ring is 1.75", and goes around just the cock. The smaller ring is 1.5", and is just for the balls. If you normally wear a 2" diameter cock ring (or slightly smaller), this would be your size.