This thing allows you to mount a Makerbot direct drive extruder clone onto a prusa i3 x carriage sideways so you do not lose as much Y print area. Use the 4 holes to run screws into the back of your stepper motor (you will need slightly longer screws than the ones that come in it.) the pegs on top and bottom are for zip tying wires. The second file includes an optional fan mount for your extruder motor. I had a 14mm heat sink laying around so it is spaced to fit that.