I started with the revised fully printable eggbot here http://www.thingiverse.com/thing:20398 and found the servos on hand didn't fit well and had to work too hard. There was also some backlash in the original pen design that I could only fix by crushing the pen so the pen holder has had some adjustments made. Make an eggbot attach these parts in place of the originals. I have to rotate them in before slicing and the servo does need support. My purpose was to remove as much backlash as I could and make a more accurate eggbot. This is an "upgrade" to Glasswalkers eggbot pen arm. A better term might be this is a specialization of the original. The shaft mount is not included but I am still using the original. The pen securing bolts and nuts are sized for m3x8 and are sized tight enough that a nut may not be needed. The slider bolt slot is also m3. The pen aperture will not fit a normal sharpie, but will fit the art type ink pens or a sharpie fine. The servo mount is for a 9g hobby servo I got for 3$ at the rc store