This is a sizing kit I used only once to test my ring size prior to purchasing the Oura. Oura Ring sizes are slightly different from standard ring sizes, so it is important to size yourself using the tools and to follow our sizing instructions. The Oura Ring Sizing Kit allows for you, and those around you, to find the ideal fit before purchasing. A properly fitting Oura Ring will result in the highest possible data accuracy, comfort, and overall experience.