This is a modified design based on the original printrbot x-axis carriage. It's much stronger and uses four bearings rather than two. It has built in belt attachment/clamp surfaces. It has a wider surface for attaching to the extruder mount (designed for my modified extruder mount).I have included the sketchup so you can adjust to fit your specific needs or modify it (for example adjusting the tightness of the press-fit holes for the bearings).