Easy print, I screwed up the layer height color change to show the text better.

Looking at the .stl model the slot in the clamp bodies is 3.9mm by 17.150mm. In inches 0.15" by 0.68". We only have imperial sized steel around here. I would guess the closest material to this is 1/8" by 5/8" stock. (0.125" by 0.625") I expect that sized steel stock would be a bit small. What size in metric stock might be a better fit?

What is meant by "comercial size steel bar", what size is this I understand the length is variable. What are the width & length of the bar that it's been designed for?