Size Reference

Size 7 =Inner diameter 17mm = 53.4 mm Inner circumference
Size 8 =Inner diameter 18mm = 56.5 mm Inner circumference
Size 9 =Inner diameter 19mm = 59.7 mm Inner circumference
Size 10 =Inner diameter 20mm = 62.8 mm Inner circumference
size 11 =Inner diameter 21mm = 66 mm Inner circumference
size 12 =Inner diameter 22mm = 69 mm Inner circumference
size 13 =Inner diameter 23mm = 72.3 mm Inner circumference