This linear bearing consists of 5 races, which are printed separately. Each race contains 18 (copper) balls of 3.2 mm. I got the balls from the Dutch "Huis en Comfort" site: http://www.huis-en-comfort.nl/Glasreiniger-kogeltjes-480899.html?group=765764. If you want to use a bit larger diameter tube, you only have to design the outer housing yourself (the pentagon-like thing) and make it a bit larger. The races will fit in the corners and give a nice smooth run. Have Fun!The ball channel is only 0.4 mm larger than the actual ball size. As you can imagine, you need a nice smooth print. So make sure that your printer is properly calibrated and does not use too much plastic. Too little is better than too much in this case! I printed my races with a 10% decrease in flow compared to normal (calibrated) operation.