Lightweight five spoke wheel for 28BYJ-48 stepper motor. Diameter is 84 mm. Set screw hole for M3 screw. The part was constructed using antimony ( http://www.mattkeeter.com/projects/antimony/3/ ) which is a new, absolutely fantastic, CAD program using graphs to design the part. See the attached image of the graph. For use with something like the apogee robot: http://www.thingiverse.com/thing:648394Print. Install. Use a M3 or 1/8" set screw. I printed mine w/ .8 thick walls and 10% infill.