This is the makerbot spring-loaded extruder, but customised to fit the CTC Replicator Dual Printer. It uses the Gear of the original extruder. I also made the bearing fixed with a screw because the original plastic piece looked way to weak.The cover fits a normal M3 screw head. You need a 8 mm M3 screw for the bearing, 16 mm M3 screw for the lever, 5 mm M3 countersunk screw (you can use the original and cut it) for the second screw to the motor. You also need 3 M3 washers. One is for the screw at the lever. Two for the bearing (you have to cut a bit of the material on the cover piece to fit perfect). The spring has to be 10 mm in diameter. I used 32mm x 10mm and cut it to 30mm x 10mm. Then it has pretty hard pressure. When you install the extruder you should stick a bit of tape to the back of the heat sink which isolate the metal parts from each other, because they will make very annoying noises while printing. But make sure the tape is not between the alu block in the bottom and the heat sink, because than it won't cool it right. Because it got requested, here are the STL files of both extruders. Each extruder consists of the three parts: you can download each part separate. When you want to print ABS in a heated closed chamber you should print the extruder in ABS, because PLA will deform itself after a while. PLA worked for month for me when only printing PLA in open printer.