About sizes
| UK size | Diameter (mm) |
Circumference (mm) |
| I | 15,29 | 48,0 |
| I+ | 15,39 | 48,3 |
| J | 15,49 | 48,7 |
| J+ | 15,70 | 49,3 |
| K | 15,90 | 50,0 |
| K+ | 16,10 | 50,6 |
| L | 16,31 | 51,2 |
| L+ | 16,51 | 51,9 |
| M | 16,71 | 52,5 |
| M+ | 16,92 | 53,1 |
| N | 17,12 | 53,8 |
| N+ | 17,32 | 54,4 |
| O | 17,53 | 55,1 |
| O+ | 17,73 | 55,7 |
| P | 17,93 | 56,3 |
| P+ | 18,14 | 57,0 |
| Q | 18,34 | 57,6 |
| Q+ | 18,54 | 58,3 |
| R | 18,75 | 58,9 |
| R+ | 18,95 | 59,5 |
| S | 19,15 | 60,2 |
| S+ | 19,35 | 60,8 |
| T | 19,56 | 61,4 |
| T+ | 19,76 | 62,1 |
| U | 19,96 | 62,7 |
| U+ | 20,17 | 63,4 |
| V | 20,37 | 64,0 |
| V+ | 20,57 | 64,6 |
| W | 20,78 | 65,3 |
| W+ | 20,98 | 65,9 |
| X | 21,18 | 66,6 |
| X+ | 21,39 | 67,2 |
| Y | 21,59 | 67,8 |
| Y+ | 21,69 | 68,1 |
| Z | 21,79 | 68,5 |
| Z+ | 22,00 | 69,1 |