I redesigned the X ends from the stock Prusa i3 to accept brass nut / lead screws that I recently bought from my 3d Printing supplier. I had alot of issues with noise and squeals with my m5 threaded rods and was tired of trying to fix it so I threw money at the problem. The center hole is 10.4mm the mounting holes are 3mm except the one that overlaps the rest of the part. those are 2.8mm in hopes that the plastic will hold the screw because you cannot add a nut.