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Convert Sizes By Country
Diameter (mm)
diameter (inches)
circumference (mm)
circumference (inches)
British/Australian
12.6
17.35
0.683
54.51
O
12.78
17.45
0.687
54.82
O 1/2
13
17.75
0.699
55.76
P
13.21
17.97
0.707
56.45
P 1/2
13.41
18.19
0.716
57.15
Q
13.61
18.35
0.722
57.65
Q 1/2
13.83
18.53
0.729
58.21
Q 3/4
14.05
18.61
0.733
58.47
R
14.15
18.69
0.736
58.72
R 1/4
14.25
18.8
0.74
59.06
R 1/2
14.36
18.89
0.748
59.34
R 3/4
14.45
19.1
0.752
60
S
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