US Size	Diameter in inches	Diameter in MM's	British	French	German	Japanese	Swiss
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 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	41 1/2	13 1/2	2	1 1/2
2 1/4	-	13.41	D 1/2	-	-
2 1/2	.536	13.61	E	42 3/4	13 3/4	3	2 3/4
2 3/4	-	13.83	E 1/2	-	-
3	.553	14.05	F	44	14	4	4
3 1/8	-	14.15	F 1/2	-	-
3 1/4	-	14.25	-	-	-
3 3/8	-	14.36	G	45 1/4	-	5	5 1/4
3 1/2	.569	14.45	-	-	14 1/2
3 5/8	-	14.56	G 1/2	-		6
3 3/4	-	14.65	H	46 1/2			6 1/2
4	.585	14.86	H 1/2	-	15	7
4 1/4	-	15.04	I	47 3/4			7 3/4
4 1/2	.601	15.27	I 1/2	-	15 1/4	8
4 5/8	-	15.40	J	49	15 1/2		9
4 3/4	-	15.53	-	-
5	.618	15.70	J 1/2	-	15 3/4	9
5 1/8	-	15.80	K	50			10
5 1/4	-	15.90	-	-
5 3/8	-	16.0	K 1/2	-		10
5 1/2	.634	16.10	L	51 3/4	16		11 3/4
5 3/4	-	16.30	-	-
5 7/8	-	16.41	L 1/2	-
6	.650	16.51	M	52 3/4	16 1/2	12	12 3/4
6 1/4	-	16.71	M 1/2	-
6 1/2	.666	16.92	N	54	17	13	14
6 3/4	-	17.13	N 1/2	-
7	.683	17.35	O	55 1/4	17 1/4	14	15 1/4
7 1/4	-	17.45	O 1/2	-
7 1/2	.699	17.75	P	56 1/2	17 3/4	15	16 1/2
7 3/4	-	17.97	P 1/2	-
8	.716	18.19	Q	57 3/4	18	16	17 3/4
8 1/4	-	18.35	Q 1/2	-
8 1/2	.732	18.53	-	-	18 1/2	17
8 5/8	-	18.61	R	59			19
8 3/4	-	18.69	-	-
8 7/8	-	18.80	R 1/2	-
9	.748	18.89	-	-	19	18
9 1/8	-	19.10	S	60 1/4			20 1/4
9 1/4	-	19.22	-	-
9 3/8	-	19.31	S 1/2	-
9 1/2	.764	19.41	-	-	19 1/2	19
9 5/8	-	19.51	T	61 1/2			21 1/2
9 3/4	-	19.62	-	-
10	.781	19.84	T 1/2	-	20	20
10 1/4	-	20.02	U	62 3/4		21	22 3/4
10 1/2	.797	20.20	U 1/2	-	20 1/4	22
10 5/8	-	20.32	V	63			23 3/4
10 3/4	-	20.44	-	-
11	.814	20.68	V 1/2	-	20 3/4	23
11 1/8	-	20.76	W	65			25
11 1/4	-	20.85	-	-
11 3/8	-	20.94	W 1/2	-
11 1/2	-	21.08	-	-	21	24
11 5/8	.830	21.18	X	66 1/4			26 1/4
11 3/4	-	21.24	-	-
11 7/8	-	21.30	X 1/2	-
12	.846	21.49	Y	67 1/2	21 1/4	25	27 1/2
12 1/4	-	21.69	Y 1/2	-
12 1/2	.862	21.89	Z	68 3/4	21 3/4	26	28 3/4
12 3/4	-	22.10	Z 1/2	-
13	.879	22.33	-	-	22	27