By Brigitte Jewellery Size (Australia / UK) Inside Diameter (mm) USA / Canada Size
D 13.1
D 1/2 13.3 2
E 13.5
E 1/2 13.7 2.5
F 13.9
F 1/2 14.1 3
G 14.3
G 1/2 14.5 3 1/2
H 14.7
H 1/2 14.9 4
I 15.1
I 1/2 15.3 4 1/2
J 15.5
J 1/2 15.7 5
K 15.9
K 1/2 16.1 5 1/2
L 16.3
L 1/2 16.5 6
M 16.7
M 1/2 16.9 6 1/2
N 17.1
N 1/2 17.3 7
O 17.5
O 1/2 17.7 7 1/2
P 17.9
P 1/2 18.1 8
Q 18.3
Q 1/2 18.5 8 1/2
R 18.8
R 1/2 19 9
S 19.2
S 1/2 19.4 9 1/2
T 19.6
T 1/2 19.8 10
U 20
U 1/2 20.2 1O 1/2
V 20.4
V 1/2 20.6 11
W 20.8
W 1/2 21 11 1/2
X 21.2
X 1/2 21.4 12
Y 21.6
Y 1/2 21.8 12 1/2
Z 22
Z 1/2 22.2 13
Z+1 22.4
Z+1 1/2 22.6 13 1/2
Z+2 22.8
Z+2 1/2 23.95 14
Z+3 23.15