The base wheels in the Ingocraft toy set have a problem: They don't connect to anything. They spin nicely -- very nicely -- around the smooth part of a long bolt, but you can't drive them with anything, and you can't translate their motion to anything else. The threaded holes in this solid wheel attempt to fix that. This is a normal Ingocraft wheel filled in and then hollowed out with threading appropriate for Ingo bolts.Printed at .2mm on a Prusa i3v from Makerfarm, no supports or brim. I used a standard Ingo bolt to "grind out" the threading a bit post-printing, but that could just be a quirk of my printer.