Printable Linear Bearing and Rail System - Draft 2

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.