About the size notation of the ring

Japanese China	America	England	France
No. 7	4	H	47.1 mm
No. 8	4 1/2	I	48.2 mm
No. 9	5	J	49.2 mm
No. 10	5 1/2	K	50.3 mm
No. 11	6	L	51.3 mm

Japanese China	America	England	France
No. 12	6 1/2	M	52.4 mm
No. 13	7	N	53.4 mm
No. 14	7 1/2	O	54.5 mm
No. 15	8	P	55.5 mm
No. 16	8	P	56.6 mm