30mm By 1.4 nut

I need a special nut for my cnc convertion of my lathe. The nut
size is (30mm by 1.4). The outside diameter of the threads the nut
will fit on is (29.75mm). What I need to know is what size do I
bore the nut out to before threading? I plan to use a single tooth
thread endmill. I have played a little with this feature of my mill
but have no real experience with it. how deep do I mill to?

Thanks
Brian