This is a tool for the Replicator 2X to help hold the extruder heaters in place while unscrewing the nozzle.
The only way I have found to remove the nozzles without turning the heater itself and damaging the wires is by first bracing the cylindrical heater cartridges on the back side of the heater block.
This tool does just that: it prevents the heaters from twisting while unscrewing the extruder nozzles by bracing them against the carriage itself. Just slide it up into place on the back side of the heaters between the belt and break the nozzles loose with a small (7mm seems to fit) wrench.
NOTE: DO NOT USE WITH THE HEATERS ON OR IT WILL MELT!!!!