This is a customisable version of the pen holder arms used by EggBots (http://shop.evilmadscientist.com/productsmenu/51-accessories/205-distalarm). It was designed to be a solid, one piece object without any nuts and bolts for holding it together. It actually turned out to be 2 pieces glued together, as it's easier and faster to print this way. To allow fitting different kinds of pens (for example Sharpie Ultrafine and Sharpie Fine markers), the pen arm itself contains a hole for an pen adaptor module. This way, when you want to change pens, you only need to replace the adaptor with another one and you get a tight fit on any pen of yours. I supplied STLs for adaptors for the ultrafine Sharie and for the fine-point Sharpie. If you want to use a custom pen, a configurable OpenSCAD file is available where you can change the diameters around. The OpenSCAD file also allows the customization of various parameters, like the length of the arm, the thickness of the piece and the diameter of the bolt fixing the pen. Extra parts needed: Compatible with Basic, Deluxe and Ostrich EggBots. You can use the same S90 TowerPro servo on this arm as on the one you got from EvilMadScientist. Update 1 @ 2015-04-12 The supplied STL files have been generated from the OpenSCAD file. They are configured for a standard EggBot, for use with an M3 bolt and nut as pen fixers and contain adaptors for the ultrafine Sharpie and the fine Sharpie markers. Pretty straightforward. If you want to customize it, take a look at the SCAD file, it even has comments. The most important settings in it: At the end of the OpenSCAD file you will find module calls that you can comment out to obtain the specific parts you want.