| UK Size | US Size |
Inside Diameter (mm) |
Circumference (mm) |
| H | 4 |
14.8 |
46.8 |
| I | 4.5 |
15 |
48 |
| J | 4.75 |
15.4 |
48.5 |
| J 1/2 | 5 |
15.7 |
49 |
| K 1/2 | 5.5 |
16 |
50.6 |
| L 1/2 | 5.75 |
16.5 |
51 |
| M | 6 | 15.5 | 52 |
| M 1/2 | 6.5 | 16.9 | 53 |
| N | 6.75 | 17 | 53.7 |
| N 1/2 | 7 | 17.3 | 54.4 |
| O 1/2 | 7.5 | 17.7 | 55.7 |
| P 1/2 | 8 | 18.1 | 57 |
| Q 1/2 | 8.5 | 18.5 | 58.3 |
| R 1/2 | 9 | 18.9 | 59.5 |
| S 1/2 | 9.5 | 19.3 | 60.8 |
| T 1/2 | 10 | 19.7 | 62 |
| U 1/2 | 10.5 | 20.1 | 63 |
| V 1/2 | 11 | 20.6 | 64.5 |