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My Zero S was the same way. My Hudy tools wouldn't fit in the 2mm screw heads. They were all undersized. You should be using a hex driver to make your life easier though, but thats no guarantee it's going to fit their screws like it should. This is one of the problems with buying these super cheap kits. They have no QC. So you get what you get.
Another solution would be to just replace the screws.
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