This is a block you can put in if you decide to remove one of your extruders on a FlashForge Replicator. Having less weight on the Gantry will improve both your X and Y precision. The assembly removed is more than 25% of the total weight being moved by your y-axis and about 40% less weight being moved by your X-axis stepper during every print head movement. In technical jargon, it will reduce your "backlash". You need this block to enable the tightening of the 2 screws on the bracket above. Otherwise they will just tip towards the location where the extruder used to be and cause alignment issues for your filament tube on the right extruder.I made mine out of PLA (it doesn't get very hot in this location) and 50% fill.