Find your right size with the Oura Ring 4 Sizing Kit. The kit includes 12 plastic rings, from size 4 to 15. Wear a plastic ring for a full day to see how the ring performs in different everyday situations. When you make a fist, there should be no gap between the ring and the skin, but it should also not be too tight. The kit is brand new and in its original packaging. It has been opened because it was used for sizing, but only once!