Because all the screws are standard/imperial. Not sure what screw you are trying to loosen or tighten. I don't have the hardware list in front of me, but I think most hardware was under 4-40. So going to need some small wrenches. Off hand, I would say you will likely need .050", 1/16", 5/64", 3/32" and possibly a 7/64". I will look for the hardware tomorrow and get you a more definitive answer then.