Pen Adapter for EggBot

When I built my first Eggbot the pen arm design was influenced by the [distal pen arm (thing:696294)](https://www.thingiverse.com/thing:696294). This design already allowed to clamp different pens to the same center positon by providing adapters with different diameters. But it has two other disadvantages it shares with most pen holders, namely:

- The pens are directly clamped with a screw. This could damage the pens and cause the cap not fit tight any more.
- If you want to print your egg with different colors, then it is difficult to adjust the pens always to the same length.


The pen adapter in this design solves these issues. Using these adapters the tip of the pens are always centered and at the same depth.