Many cheap 3 d printers have the Z axis climbing up and down on threaded rods, one end (usually the bottome one) attached to the stepper motor, the other one.... free to wobble.

And this causes some issues with the printing process.

Locking the other end from wobbling is something that actually improves the quality of printing, hence here you can download and print the supports, their lid, and you need to go buy online some bearings I.D. 8mm, O.D. 22mm, widht 7 mm or near by.

Lock the bearig into the support, snug fit the bearing on the rod, align perfectly in vertical with the stepper motor axis, and bolt it to the frame.  If it is excedingly going out the frame, just cut it by the frame with a saw than superglue a trasversal bit to keep the thinghy from snapping loose under the presure of the bolts.  I have no clue what printer you are going to fit those onto, so I made a them pretty generous locking platform.