I made this part to improve the accuracy of the z-axis stop screw. This part exist in two version : the large one and the small one. I only printed the small one and it is stable enough. You can use the original screws except, the setting screw that I replaced with a larger one. The stop switch is mounted on this http://www.thingiverse.com/thing:232446 You need : Put the spring between the two nuts into the socket at the back. Screw the setting screw to hold the nuts in place. Screw the holder to the extruder arm with originals screws.