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!!