In my quest of building a Maxi kossel with 2020 extrusion, i've tested these http://www.thingiverse.com/thing:566093 with POW shower roller. i found that the carrier wobbling a little bit. i've try with 608 bearing, but metal on metal is too noisy for me. So instead of paid 80€ for proper delrin rollers. I've try to made my own with a bunch of MR83-ZZ bearings. theses rollers can be printed in pla or flex. PLA works but i try to make the kossel as quiet as possible. (ecco)Flex roller a smoother and make no noise but even at 100% infill it have a tendecy to bend and make delta printer inacurate. ps: Print settings E3D 0.4 nozzle, 0.15 layer height, 4 perimeters, 100% infill speed 60mm/s.