In article , yourname wrote:
Now wait, you can use the thread dial with odd pitch threads[3 1/2 for
instance], as long as you always return to the same number, it makes no
sense to me that metric would be any different.

THink about it this way. If you open the half nuts and move the carriage
until the dial rotates one full turn and then close the half nuts
you have moved the carriage some increment of the lead screw pitch.
Probably 1 inch in this case. IF you are threading a .8 MM pitch
will the toolbit still line up with the thread. No way.

chuck