Ring Dia ⌀ (Inside)		Ring Circumference (Inside)		‹ International Standard Sizes ›
MM	Inches	MM	Inches	UK / AU	USA / CA	Europe
9.9	0.390	31.1	1.22	·	0000	·
10.7	0.442	33.7	1.39	·	00	·
11.5	0.454	36.2	1.43	·	0	·
12.0	0.470	37.5	1.50	A	1/2	·
12.2	0.479	38.3	1.51	A 1/2	3/4	·
12.4	0.487	38.9	1.53	B	1	·
12.6	0.506	39.6	1.56	B 1/2	1 1/4	·
12.8	0.503	40.2	1.58	C	1 1/2	·
13.0	0.511	40.8	1.61	C 1/2	1 3/4	·
13.2	0.520	41.5	1.63	D	2	41 1/2
13.4	0.528	42.1	1.66	D 1/2	2 1/4	·
13.6	0.536	42.8	1.68	E	2 1/2	42 3/4
13.8	0.544	43.5	1.71	E 1/2	2 3/4	·
14.0	0.553	44.1	1.74	F	3	44
14.2	0.557	44.5	1.75	F 1/2	3 1/8	·
14.3	0.561	44.8	1.76	F 3/4	3 1/4	·
14.4	0.565	45.1	1.77	G	3 3/8	45 1/4
14.5	0.568	45.4	1.79	G 1/4	3 1/2	·
14.6	0.573	45.7	1.80	G 1/2	3 5/8	·
14.7	0.576	46.0	1.81	H	3 3/4	46 1/2
14.9	0.585	46.7	1.84	H 1/2	4	·
15.0	0.592	47.3	1.86	I	4 1/4	47 3/4
15.3	0.601	48.0	1.89	I 1/2	4 1/2	·
15.4	0.606	48.4	1.90	J	4 5/8	50
15.5	0.611	48.8	1.92	J 1/4	4 3/4	·
15.7	0.618	50.3	1.94	J 1/2	5	·
15.8	0.622	50.6	1.95	K	5 1/8	50
15.9	0.625	50.0	1.97	K 1/4	5 1/4	·
16.0	0.630	50.3	1.98	K 1/2	5 3/8	·
16.1	0.634	50.6	1.99	L	5 1/2	51 3/4
16.3	0.642	51.2	2.02	L 1/4	5 3/4	·
16.4	0.646	51.6	2.03	L 1/2	5 7/8	·
16.5	0.650	51.9	2.04	M	6	52 3/4
16.7	0.658	52.5	2.07	M 1/2	6 1/4	·
16.9	0.666	53.2	2.09	N	6 1/2	54
17.1	0.674	53.8	2.12	N 1/2	6 3/4	·
17.4	0.683	54.5	2.15	O	7	55 1/4
17.5	0.687	54.8	2.16	O 1/2	7 1/4	·