Summary

Made almost the same changes as here:
http://www.thingiverse.com/thing:337630

However, I used 123D Design for adding a nut and supports, and the STL file is much, much smaller - 4 mb instead of 81 mb (my computer failed to open such a big STL). The place for the nut is also geometrically correct in this version.

The supports are a bit stronger and have to be cut out.