Ring Size Gauge 7-7.5 (American)

thingiverse

The first hole near the "7" is size 7, the next hole is size 7.25, then 7.5, and the farthest is 7.75. I printed this in PETg, which contracted by 0.13 mm when it cooled off, which is roughly equivalent to 0.125 of a size, so each hole size is slightly small. Probably not good enough for professional use, but better than using string and then measuring the string with a ruler!