Ring Conversion Chart
| Inner Diameter (mm) | EU / FRANCE | SPAIN / ITALY | GERMANY | SWITZERLAND | UK | USA |
| 15 | 47 | 7 | - | 7.75 | I | 4 1/4 |
| 15.3 | 48 | 8 | 15.25 | 8 | J | 4 3/4 |
| 15.6 | 49 | 9 | 15.75 | 9.5 | J 1/2 | 5 |
| 15.9 | 50 | 10 | 16 | 10.75 | K | 5 1/4 |
| 16.2 | 51 | 11 | - | - | L | 5 3/4 |
| 16.5 | 52 | 12 | 16.5 | 12.75 | M | 6 1/4 |
| 16.8 | 53 | 13 | 17 | 14 | M 1/2 | 6 1/2 |
| 17.2 | 54 | 14 | 17.25 | 15.25 | N 1/2 | 7 |
| 17.5 | 55 | 15 | - | - | p | 7 1/2 |
| 17.8 | 56 | 16 | 17.75 | 16.5 | - | - |
| 18.1 | 57 | 17 | 18 | 17.75 | Q | 8 |
| 18.4 | 58 | 18 | 18.5 | 18.5 | R | 8 1/2 |
| 18.8 | 59 | 19 | - | - | S | 9 |
| 19.1 | 60 | 20 | 19 | 20 | T | 9 1/2 |
| 19.4 | 61 | 21 | 19.5 | 21 | - | - |
| 19.7 | 62 | 22 | 20 | 21.75 | U | 10 |
| 20 | 63 | 23 | - | 22.75 | V | 10 1/2 |
| 20.4 | 64 | 24 | - | 23.75 | W | 11 |
| 20.8 | 65 | 25 | 25 | X | 11 1/2 |
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