Item: Oura Ring Gen3 Sizing Kit; Sizes 6,7,8,9,10,11,12,13; Heritage model Description: Sizing Kit for Oura Ring Gen3 models. Oura ring sizes differ from standard ring sizes, so if you intend to purchase an Oura ring (either new or used) it’s important to use this sizing kit to determine proper fit for optimal device accuracy and performance. Condition: New