Jonas Kuehling Improved X-Ends for RepRap Printers for a 6mm Threaded rod to eliminate Z-wobble. Combine this with switching to flexible Vinyl (or Vulcanized rubber) Z-Axis Motor Couplers and your part quality immediately jumps higher.
Print directly the the STL FIles, that are cleaned and ready to go, or Edit the Scad File, Like I did to make even more changes. I took Jonas Kuehling's original Scad File and changed the variables to make it for 6mm threaded rods for the Z-Axis Lead Screws. You could use 1/4" - 28 rods as a close replacement, or 6mm x 1mm Rods like we do, or 1/4" x 20 Threaded rods for a more course Z step (but cheapest threaded rod in the US).
At the same time, throw out your old motor couplers, and switch over to a flexible vinyl tubing for your Z motor Couplers (from the 5mm Nema 17 motor shaft to the new 6mm Z axis threaded rod), and your print quality will be considerably higher. Do make sure that the new 6mm rods are totally straight. Test them by rolling them on a flat table prior to installation, they should roll freely without assistance other than maybe an initial push. If they hesitate, you have a bent threaded rod, get another one, don't try to unbend it - unbending rarely goes well.
Everyone talks about upgrading to 6mm threaded rods, but no one uploaded the X-Ends to do this... Until now.