US  Size

Dia.in inch

Dia. in MM

British 

0000

.390

9.91

-

00

.422

10.72

-

0

.454

11.53

-

1/2

.474

11.95

A

3/4

.482

12.18

A 1/2

1

.487

12.37

B

1 1/4

-

12.60

B 1/2

1 1/2

.503

12.78

C

1 3/4

-

13.00

C 1/2

2

.520

13.21

D

2 1/4

-

13.41

D 1/2

2 1/2

.536

13.61

E

2 3/4

-

13.83

E 1/2

3

.553

14.05

F

3 1/8

-

14.15

F 1/2

3 1/4

-

14.25

-

3 3/8

-

14.36

G

3 1/2

.569

14.45

-

3 5/8

-

14.56

 G 1/2

3 3/4

-

14.65

H

4

.585

14.86

H 1/2

4 1/4

-

15.04

I 

4 1/2

.601

15.27

I 1/2

4 5/8

-

15.40

J

4 3/4

-

15.53

-

5

.618

15.70

J 1/2

5 1/8

-

15.80

K

5 1/4

-

15.90

-

5 3/8

-

16.0

K 1/2

5 1/2

.634

16.10

L

5 3/4

-

16.30

-

5 7/8

-

16.41

L 1/2

6

.650

16.51

M

6 1/4

-

16.71

M 1/2

6 1/2

.666

16.92

N

6 3/4

-

17.13

N 1/2

7

.683

17.35

O

7 1/4

-

17.45

O 1/2

7 1/2

.699

17.75

P

7 3/4

-

17.97

P 1/2

8

.716

18.19

Q

8 1/4

-

18.35

Q 1/2

8 1/2

.732

18.53

-

8 5/8

-

18.61

R

8 3/4

-

18.69

-

8 7/8

-

18.80

R 1/2

9

.748

18.89

-

9 1/8

-

19.10

S

9 1/4

-

19.22

-

9 3/8

-

19.31

S 1/2

9 1/2

.764

19.41

-

9 5/8

-

19.51

T

9 3/4

-

19.62

-

10

.781

19.84

T 1/2

10 1/4

-

20.02

U

10 1/2

.797

20.20

U 1/2

10 5/8

-

20.32

V

10 3/4

-

20.44

-

11

.814

20.68

V 1/2

11 1/8

-

20.76

W

11 1/4

-

20.85

-

11 3/8

-

20.94

W 1/2

11 1/2

-

21.08

-

11 5/8

.830

21.18

X

11 3/4

-

21.24

-

11 7/8

-

21.30

X 1/2

12

.846

21.49

Y

12 1/4

-

21.69

Y 1/2

12 1/2

.862

21.89

Z

12 3/4

-

22.10

Z 1/2

13

.879

22.33

-