Linear Bearing for Airsoft BBs

I was working on a derivative of: http://www.thingiverse.com/thing:5830 when I realized I could make a printable linear bearing for it.

This is that bearing. It provides three inner racetracks rolling against the inner axle. The length is adjustable to increase the number of ball bearings in contact with the inner axle. Longer length will be more stable therefore.

To approximate the stability of the reprap based xy rider designs, you'd want at least two of these 35mm or greater in lengt