Thanks for the pointers and the maths but I will be using what is at hand or can be begged / borrowed.
I will certainly not be investing in any triple or Quad threading tools.
Nor a metal turning lathe.
The whole experiment is a suck it and see exercise.
However if it is such a raving success as my bling pens are :nonono::nonono::nonono:
I may progress to bigger better faster more. 
The information above will certainly be useful to anyone else who may wish to pursue this avenue.