This is the second draft of work towards a linear bearing and rail system containing only one non-printed part, the rolling elements (6mm airsoft BBs). Why airsoft BBs? They're cheap, they're round, they're biodegradable, and they're easy to get.The system is currently at the "workingish" stage of development. The original draft from a year ago proved to have some major problems when I finally was able to print it, so I threw a lot of stuff from it out and focused on getting something that rolled. As a result, there are 3 non-printable parts in this thing - the balls, M3 screws left over from my makerbot assembly, M3 nuts to go with them. I printed it and it rolls alright, with a bit more play than I'm really happy with. If your tolerances are better/different from mine, you will probably get different results.The bearing itself is made of 2 Half-Bearing pieces, 1 Retainer piece, 2 M3 screws, 2 nuts, and 32 BBs (16 in each race). BBs can be inserted during assembly, or after assembly by pushing them in between the retainer and the bearing. Chances are some will fall out and need to be pushed back in at some point.If you're printing this, I recommend starting with 2 Half Rail pieces and 2 Rail Brace pieces. M3 screws should pass through the holes in the rails and thread into the braces, but your mileage may vary. This should be enough to check if the parts are coming off your machine in working order. To expand the rail by one length, print 2 Half Rail pieces and one Rail connector piece. Replace one brace with one end of the connector and move the brace to the new end of the rail. The image I posted is 3 lengths long, containing 6 Half Rail pieces, 2 Connectors, and 2 Braces in total.