Summary

This Thing is meant to be a "rack and pinion type thing" to replace the lower belt drive on a Printrbot. The rubber belt can stretch over time and crack or dry out easily from the heat of the bed. Align it with your lower Y-Axis Stepper Motor, and screw in place with three screws. Place two of these in series for a full length Get-Rid-Of-Belts-On-Printrbot-Thing!!

Instructions

Print out two pieces with 100% infill and 0.27 mm resolution or better.
Sand down rough edges with fine grit sandpaper where necessary. We need to make sure we have a smooth surface here or else we will get jittery prints.
Remove old belt drive on bottom of Printrbot (Y-Axis belt) as well as the washer tensioner Thing (This will be in the way for the new parts).
Align new printed parts in place with existing gear (on the left side of the belt), and fasten to printrbot with screws making sure not to screw into heated bed. Determine correct length screws for your printer BEFORE screwing.
Move bed forward and backwards to determine if it is adjusted properly and straight.
Once straight, VOILA! You now have a thing to create more accurate parts and to get rid of those annoying belts that always stretch and get too loose!!

Bryan-Enjoy!