I only used 8mm round bar because I had a little bit there in the "bits-bin" and typically a bolt is minimum 8.8 hardness so too hard to drill out.You really is a clever bugga.
I read all this stuff, have no idea what a lot of it is about, but still love reading it!
Could you not have just bought some threaded bar and then drilled the hole in the end, or did you want the bar to have a bit with no thread on it so as to keep it dead straight in whatever will be holding it?
a length of M8 studding could also have been used, but that would have been 1/2 the fun