Summary

In my apartment shower, the knob used to tighten the holder to the vertical rod had become loose due to tear and wear in the thread, so of course a new one had to be produced.

I used the following libraries:
http://dkprojects.net/openscad-threads/
http://www.thingiverse.com/thing:32122

The knurled part takes almost forever to render in OpenSCAD, but the result speaks for itself: Awesome!