Question #3 about the Robonova kit?

In the assembly of the ankle and thigh brackets you use four screws each. I think that using bolts with nuts and washers would work best here, not sure? The stress on the hip or thigh bracket has to be high? I am going to check out my local hardware store. Is the problem that the screws or so small and that there is not enough room for a nuts and bolts? I have to check this out.