Revised to v1.3 - Stronger, Drilled out, larger Dia. Wheel
The fastener is in two parts and are just glued, they are based upon an M5x30 Lg bolt and M5 nut, the heads are about 3.5mm thick.
See my youtube video for more info. http://youtu.be/28XyvYgU04U
I use Cura on my Ultimaker Original to prepare the print.
Free Download of Cura http://software.ultimaker.com/
I printed at 0.2 layer height
%100 infil - just because its untested for strength in the cold and i need something to last.