Inside diameter (mm) Inside circumference (mm) United States and Canada UK, Ireland, Australia and New Zealand China, Japan, South America Italy, Spain, Netherlands, Switzerland
14.07 44.2 3 F 4 4.25
14.27 44.8 3 1/4 F 1/2 5 4.75
14.48 45.5 3 1/2 G 5.5
14.68 46.1 3 3/4 G 1/2 6 6
14.88 46.8 4 H 7 6.75
15.09 47.4 4 1/4 H 1/2 7.5
15.29 48 4 1/2 I 8 8
15.49 48.7 4 3/4 J 8.75
15.7 49.3 5 J 1/2 9 9.25
15.9 50 5 1/4 K 10
16.1 50.6 5 1/2 K 1/2 10 10.5
16.31 51.2 5 3/4 L 11.25
16.51 51.9 6 L 1/2 11 11.75
16.71 52.5 6 1/4 M 12 12.5
16.92 53.1 6 1/2 M 1/2 13 13.25
17.12 53.8 6 3/4 N 13.75
17.32 54.4 7 N 1/2 14 14.5
17.53 55.1 7 1/4 O 15
17.73 55.7 7 1/2 O 1/2 15 15.75
17.93 56.3 7 3/4 P 16.25
18.14 57 8 P 1/2 16 17
18.34 57.6 8 1/4 Q 17.5
18.54 58.3 8 1/2 Q 1/2 17 18.25
18.75 58.9 8 3/4 R 19
18.95 59.5 9 R 1/2 18 19.5
19.15 60.2 9 1/4 S 20.25
19.35 60.8 9 1/2 S 1/2 19 20.75
19.56 61.4 9 3/4 T 21.5
19.76 62.1 10 T 1/2 20 22
19.96 62.7 10 1/4 U 21 22.75
20.17 63.4 10 1/2 U 1/2 22 23.25
20.37 64 10 3/4 V 24
20.57 64.6 11 V 1/2 23 24.75
20.78 65.3 11 1/4 W 25.25
20.98 65.9 11 1/2 W 1/2 24 26
21.18 66.6 11 3/4 X 26.5
21.39 67.2 12 X 1/2 25 27.25
21.59 67.8 12 1/4 Y 27.75
21.79 68.5 12 1/2 Z 26 28.5
22 69.1 12 3/4 Z 1/2 29
22.2 69.7 13 27 29.75