I really liked the design of ei8htohms "Olde Timey Spur Gear for Printrbot Extruder" (thing:163975) so I adapted it for the Printrbot Simple Metal.
Made it a bit smaller and thinner, because it's now just an accessoire.
Also added a mount for the shaft of the extruder. (Holes are actually a bit too big in the files, but came out just right with my simple metal.)
Printed in colorFabb Traffic Red PLA/PHA.
Printed in colorFabb Traffic Red PLA/PHA with Printrbot Simple Metal on blue tape (This filament stick extremly well to it, maybe even too well)
Support: 15% (More will result in better print!)