This is a sizing kit for the Oura Ring before purchasing the main unit. Oura Ring sizes: 6, 7, 8, 9, 10, 11, 12, 13 Used only once before ordering an Oura Ring. Please refrain from purchasing if you are concerned about home storage. This is for generation 3, one generation before the latest. It's perfect for verifying whether you can wear the Oura Ring 24 hours a day without any issues.