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ring size (us) inside circumference (mm)  inside diameter (mm)
7 54.4 17.3
7.5 55.7 17.7
8 57.0 18.1
8.5 58.3 18.5
9 59.5 19.0
9.5 60.8 19.4
10 62.1 19.8
10.5 63.4 20.2
11 64.6 20.6
11.5 65.9 21.0
12 67.2 21.4
12.5 68.5 21.8
13 69.7 22.2