Request for two small steel rod-esque lathed part!

[BillTodd]

Does Part2 turn with the magnet ? - I'd worry about the run-out of the M8 thread coupling. If it doesn't I suggest you make it turn with the other end, else the coil will drag.

Drilling a 0.5mm hole more than a few mm deep might prove interesting. Presumably you only need the hole to be 0.Xmm near the coil end, so most of the length of the hole could be larger. Actually, a slot might be of more use than a hole (saves that 'threading the needle' problem)

The magnet hole doesn't need to be flat bottomed it just needs a definite stop - have you considered having a set screw at the bottom of the hole, so the depth could be adjusted? (you could probably rely on the grub screw to attract the magnet and make the rest of the piece from Al or plastic)

[edit]

Thinking some more...

Hold the magnet in a brass collet with a smaller collet on the other end as an end stop (that way you'd get a concentric positive drive on the magnet)