Comes with all of the Oura Ring sizes US6-US13. They have the size printed into the side. (see image 2)
Please note this is not the official sizing kit provided by Oura but are printed from the official Oura print files that they have on their website. I have measured and calibrated them to the official measurements and have compared the size 7 sizing ring to my own Oura ring and it is pretty much identical (see images 3&4).