Thinking about the trapezoidal again, just changed my mind and now going for M10 x 2mm. A little bit cheaper and no micro-stepping drivers needed.

1 stepper motor rev = 200 steps @ 2mm pitch means 1 step = 0.01mm - I know you can state whatever steps per unit you want to in mach3 but this way it will keep it simpler for the beginners...

Starting to talk in numbers and equations like Irving now!