15 yards / within the length 11.5cm，
16 yards / within the length of 12cm，
17 yards / within the length 12.5cm，
18 yards / within the length of 13cm，
21 yards / within the length 13.5cm，
22 yards / within the length of 14cm，
23 yards / within the length 14.5cm，
24 yards / within the length of 15cm，
25 yards / within the length 15.5cm，
Inner length = foot length + 0.5cm
