Tinkeriffic BB Bearing

Like its predecessors, this Tinkertoy-compatible bearing system uses [ten 4.5mm BB's](http://rcm-na.amazon-adsystem.com/e/cm?lt1=_blank&bc1=000000&IS2=1&bg1=FFFFFF&fc1=000000&lc1=0000FF&t=zheng3-20&o=1&p=8&l=as4&m=amazon&f=ifr&ref=ss_til&asins=B00419J4X0) to provide smoother rotation than the stock wheels included with a Tinkertoy set.

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 t