It is a simple filament drive replacement for printers whose original filament drive has smaller dimensions than Makerbot's. I looked at thehttp://www.thingiverse.com/thing:42250 and http://www.thingiverse.com/thing:94979and found they are much bigger than I need - 42x29x15,2mm for Mbot3D Cube. So I've designed my own filament drive guide based on the respectful works mentioned above. SW2012 sources included.
Also you'll need:
1) M4x10 countersum screw
2) M3x8 countersum screw
3) bearing with internal 4mm hole and 13mm external diameter (I used original Mbot bearing taken from the printing head)
4) 9x15mm spring (I took one from the office paper puncher)
Known issues: IMHO, insufficient heat isolation from the extruder's stepper motor.