UPdate: The remixes of this item are vastly superior to what I produced. http://www.thingiverse.com/thing:795954 in particular has taken this to the next level. I would download it instead. This is a z mount for the MakerFarm i3v that helps to reduce z wobble and potentially backlash. It also frees up about 25mm of X travel because the original mounts are a little over sized. You'll need a 50mm spring to hold the nut in place but can reuse the original nuts. After you print the piece, press the original nut into the mount carrier and then insert the spring into the recess to hold it in place. You want the nut at the top of the x carriage.