I dont know what make they are, 12mm diameter ones I got from Marchant Dice which they appear not to supply now. They did say that wipers were not available so I thought I could use felt or rubber but knowing so little about ball screws i do not know.
My main job at the moment is get them all fitted. I have also wondered if the z-axis stepper will not be powerful enough to raise the head without some form of assistance.

Peter