Like its predecessors, this Tinkertoy-compatible bearing system uses ten 4.5mm BB's to provide smoother rotation than the stock wheels included with a Tinkertoy set: (http://bit.ly/1ngex61)
The center bore is just a little loose on a Tinkertoy rod (not renowned for their precision diameters in the first place) so if you really need the bearing to stick fast I recommend using a little piece of painters' tape around the rod.
It's modeled in three parts for ease of assembly, but you'll need to super glue the two halves together.
Seej patient zero. Barbie Armor Designer, artist, worst programmer ever. Mostly illiterate, but has minimal competence in spoken Mandarin. Not real clear on Ohm's law.