I wanted an tool holder for a sharpie, but liked the idea of http://www.thingiverse.com/thing:898232 , so I made an adapter for my master grip tool holder. This makes it easy to swap between a pen & the rotary tool. I made one version parametric & another specific for a sharpie in the Master grip. The Sharpie version I made uses less plastic than the parametric version & did not feel like spending the time coding this version to make it parametric. Rev8 will probably only work for 45mm & higher diameter. I made this one for 49mm OD.I did not even have to put a tightening bolt to use the pen. Here is a video showing my 1st pen plot printing a simple design I came up with. http://youtu.be/uzvzjpQcy2Q