Ball bearing without the need for a cage. But it definetely needs a lot of patience to put it together. I will tweak some minor issues to improve print quality. It's designed to fit 27 balls in three levels. Probably only two levels would also be easier for putting together, but then the bearing would loose its ability to carry also longitudal load. Update: it took me two prototypes to figure out the new version. All printing issues should be resolved. I also switched to dimensions for M5 screws, because I had no M3 at hand. By the way: the new installation concept does not need a clockmaker's hand to be assembled :) simply print, put the balls in place and screw together. Update 2: well... still doesn't seem to work. Now the gap is too wide so the balls fall out...