I had issues with the gears fitting cleanly on the spring loaded extruder so I decided to do a rebuild of iamburny's extruder herringbone gears. I wanted to add a small raised nose to space the gears away from the extruder motor slightly. I had to reverse the bed side on both gears so I could add the 1mm spacer nose to the top sides. If your Z home is very close the hex head hole may need to be cleaned as it is a fairly tight fit.