Inside Diameter (inches)

Inside Diameter (mm)

Inside Circumference (inches)

Inside Circumference (mm)

USA & Canada

British, Irish, Australian & New Zealand

European

0.458

11.6

1.438

36.5

 

 

 

0.466

11.8

1.463

37.2

 

 

 

0.474

12

1.488

37.8

 

A

 

0.482

12.2

1.513

38.4

 

A 1/2

 

0.49

12.4

1.539

39.1

1

B

 

0.498

12.6

1.564

39.7

1 1/4

B 1/2

 

0.506

12.9

1.589

40.4

1 1/2

C

 

0.514

13.1

1.614

41

1 3/4

C 1/2

 

0.522

13.3

1.639

41.6

2

D

1.5

0.53

13.5

1.664

42.3

2 1/4

D 1/2

 

0.538

13.7

1.689

42.9

2 1/2

E

2.75

0.546

13.9

1.714

43.5

2 3/4

E 1/2

 

0.554

14.1

1.74

44.2

3

F

4

0.562

14.3

1.765

44.8

3 1/4

F 1/2

5.25

0.57

14.5

1.79

45.5

3 1/2

G

  

0.578

14.7

1.815

46.1

3 3/4

G 1/2

6.5

0.586

14.9

1.84

46.7

4

H

   

0.594

15.1

1.865

47.4

4 1/4

H 1/2

7.75

0.602

15.3

1.89

48

4 1/2

I

  

0.61

15.5

1.915

48.7

4 3/4

J

9

0.618

15.7

1.941

49.3

5

J 1/2

  

0.626

15.9

1.966

49.9

5 1/4

K

10

0.634

16.1

1.991

50.6

5 1/2

K 1/2

  

0.642

16.3

2.016

51.2

5 3/4

L

11.75

0.65

16.5

2.041

51.8

6

L 1/2

12.75

0.658

16.7

2.066

52.5

6 1/4

M

12.75

0.666

16.9

2.091

53.1

6 1/2

M 1/2

14

0.674

17.1

2.116

53.8

6 3/4

N

 

0.682

17.3

2.141

54.4

7

N 1/2

15.25

0.69

17.5

2.167

55

7 1/4

O

 

0.698

17.7

2.192

55.7

7 1/2

O 1/2

16.5

0.706

17.9

2.217

56.3

7 3/4

P

 

0.714

18.1

2.242

56.9

8

P 1/2

17.75

0.722

18.3

2.267

57.6

8 1/4

Q

 

0.73

18.5

2.292

58.2

8 1/2

Q 1/2

 

0.738

18.7

2.317

58.9

8 3/4

R

19

0.746

18.9

2.342

59.5

9

R 1/2

 

0.754

19.2

2.368

60.1

9 1/4

S

20.25

0.762

19.4

2.393

60.8

9 1/2

S 1/2

 

0.77

19.6

2.418

61.4

9 3/4

T

21.5

0.778

19.8

2.443

62.1

10

T 1/2

 

0.786

20

2.468

62.7

10 1/4

U

 

0.794

20.2

2.493

63.3

10 1/2

U 1/2

22.75

0.802

20.4

2.518

64

10.3/4

V

 

0.81

20.6

2.543

64.6

11

V 1/2

 

0.818

20.8

2.569

65.2

11 1/4

W

25

0.826

21

2.594

65.9

11 1/2

W 1/2

 

0.834

21.2

2.619

66.5

11 3/4

X

 

0.842

21.4

2.644

67.2

12

X 1/2

27.5

0.85

21.6

2.669

67.8

12 1/4

Y

 

0.858

21.8

2.694

68.4

12 1/2

Z

28.75

0.866

22

2.719

69.1

12 3/4

Z 1/2

 

0.874

22.2

2.744

69.7

13

 

 

0.882

22.4

2.769

70.3

13 1/4

Z1

 

0.89

22.6

2.795

71

13 1/2

 

 

0.898

22.8

2.82

71.6

13 3/4

Z2

 

0.906

23

2.845

72.3

14

Z3

 

0.914

23.2

2.87

72.9

14 1/4

 

 

0.922

23.4

2.895

73.5

14 1/2

Z4

 

0.93

23.6

2.92

74.2

14 3/4

 

 

0.938

23.8

2.945

74.8

15

 

 

0.946

24

2.97

75.4

15 1/4

 

 

0.954

24.2

2.996

76.1

15 1/2

 

 

0.962

24.4

3.021

76.7

15 3/4

 

 

0.97

24.6

3.046

77.4

16