diamond center 4.5 -> 5.3 mm
5.4 -> 6.0 https://www.cgtrader.com/3d-print-models/jewelry/rings/engagement-ring-simple-54
7.0 -> 8.0 https://www.cgtrader.com/3d-print-models/jewelry/rings/enggagement-ring-simple-70
If you need to change the size of your finger or anything. Message me for help.