When building the D-Bot CoreXY 3Dprinter by spauda01 (http://www.thingiverse.com/thing:1001065), you need to tap M5 theads into several V-slots.

To help me keep the tapping tool centered and vertical, I designed this little tool guide that slides on top of the 2040 Vslot ends where needed.

Designed for an M5 thread tapping tool with less than 6 mm diameter, will work with similar tools of similar diameters.