Inside Diameter (mm)

Inside circumference (mm)

US

UK

Spain / Italy

Japan / China

16

50.2

5.5

K

10,5

10

16.5

51.9

6

L½

12

11

16.9

53

6.5

M½

13,5

13

17.3

54.4

7

N½

14,5

14

17.7

55.7

7.5

P

16

15

18.2

57

8

Q

17

16

18.6

58.3

8.5

R

18,5

17

19

59.5

9

S

20

18

19.4

61

9.5

T

21

19

19.8

62.2

10

U

22,5

20

20.2

63.4

10.5

V

23,5

22

20.6

64.7

11

W

25

23

21

66

11.5

W¾

26

24

21.4

67.2

12

Y

27,5

25

21.8

68.5

12.5

Z

29

26

22.2

69.7

13

Z+1

30

27

23

72.2

14

Z+3

33

-

24

75.4

15

Z+4

35

-