I sometimes thread socket head capscrews directly into PLA. These will self tap into a slightly undersized hole. The ANSI screws work a little better for this than metric screws because the threads are coarser. I know that the screw counts are off. My philosophy was that since it is often cheaper to buy box quantities (at least in my hardware stores), I just buy them in quantity and have them on hand. This design is nearly two years old, and I never had any idea that so many people would make this printer. I am working on refinements to the low mass extruder, and never seem to have the time to correct the quantities. My apologies, you will end up with a bunch of extra screws. I will try to use all metric sizes and document the parts more thoroughly in future designs.