Inside diameter (mm)	USA	UK	China India	European
11.63	0
11.84	¼
12.04	½	A
12.24	¾	A½
12.45	1	B	1
12.65	1¼	B½
12.85	1½	C
13.06	1¾	C½		41
13.26	2	D	2	42
13.46	2¼	D½
13.67	2½	E	3	43
13.87	2¾	E½
14.07	3	F	4	44
14.27	3¼	F½	5	45
14.48	3½	G
14.68	3¾	G½	6	46
		H		47
14.88	4	H½	7
15.09	4¼	I		48
15.29	4½	I½	8
15.49	4¾	J		49
15.7	5	J½	9	50
15.9	5¼	K		51
16.1	5½	K½	10
16.31	5¾	L		52
16.51	6	L½	11
16.71	6¼	M	12	53
16.92	6½	M½	13
17.12	6¾	N		54
17.32	7	O	14	55
17.53	7¼	O½		56
17.73	7½	P	15
17.93	7¾	P½		57
18.14	8	Q	16
18.34	8¼	Q½		58
18.54	8½	R	17	59
18.75	8¾	R½
18.95	9	S	18	60
19.15	9¼
19.35	9½	S½	19	61
19.56	9¾	T
19.76	10	T½	20	62
19.96	10¼	U	21
20.17	10½	U½	22	63
20.37	10¾	V		64
20.57	11	V½	23
20.78	11¼	W		65
20.98	11½	W½	24
21.18	11¾	X		66
21.39	12	Y	25	67
21.59	12¼	Y½		68
21.79	12½	Z	26
22	12¾	Z½		69
22.2	13		27
22.4	13¼
22.61	13½
22.81	13¾
23.01	14
23.22	14¼
23.42	14½
23.62	14¾
23.83	15
24.03	15¼
24.23	15½
24.43	15¾
24.64	16