>>/53828/
I have a good one for berts, pic related is the nut that holds my derailleur hanger to my frame.
Some stupid lapierre proprietary crap instead of just a normal bolt like a sane company would do.
Anyway the tool is sold on one (!) website I could find and cost like 40+ euros and it's just some plastic piece.
Just resorted to jamming in some allen keys and putting my weight on it to tighten it.

I hate bike manufacturers.