Why 2 Different size Springs for Hinge B
Because there are several different manufacturers that made slightly different styles with slightly different spring sizes.
If you have a heavy table top, your best bet will be to get the 127mm size as it will provide more support.
Use it with a light table top and it might not sit level at resting position because there is too much tension.
I suggest the 135mm size UNLESS your table top is heavy or the sizes of the springs are exactly what they’ll be replacing.