it is made for metrical wrench.

here is the size:

6-7_2x7mm
8-9_2x8mm
10-11_2.5x9mm
12-13_3x11mm
14-15_3.5x12.5mm
16-17_3.5x13mm
18-19_4x16.5mm
20-22_4.5x17.5mm