Here's a little something I knocked up for those of us without all the workshop tools. It's a little drill guide for drilling the mounting hole in the verticle 2020 extrusion.
It is mounted to the 2020 extrusion with a M5x10mm bolt and an Openbuilds Speed Nut.
I designed this to make life easier when building http://www.openbuilds.com/builds/onez-i3.3389/
Just align it as shown in the photo.
This thing was made with Tinkercad.