Thank you all around!

I need to make an update.

If one keeps the slug travel requirement to 1" (which isn't bad at
all, even for a broad-range PTO) and is willing to use an "outside"
micrometer (for thickness/diameter) it's a different game: micrometric
screws become really cheap! Bear in mind that repositioning trumps
absolute precision, so cheap isn't perforce bad. You can get a 0-1"
micrometer for well under $10, i.e. generally cheaper than depth
micrometers and in the ballpark for axial slow motion drives with
scales.

You can't directly drill holes in the base for front panel mounting,
as you can do in depth gauges, but the arch that positions the
reference surface opposite to the screw can be cut / drilled and used
for securing the device internally. Many models have screw-fastened
plastic grips and may not need drilling. Also, by securing it well
inside the front panel, the protrusion of the screw can be reduced.

On ebay, this search produces drossfree results:
outside micrometer -electronic -digital -laser -stage -depth -internal
-bore -torque -caliper -lea* -marking

I'll experiment with supergluing a bit of ferrite to a micrometric
screw tip with a bit of acrylic dowel in between.


On Jul 12, 8:46*pm, spamhog wrote:

- micrometric screw:
use a preexisting screw taken from old depth gauge or bought
standalone
PRO calibrated, demoltiplicated, high resolution position readout
CON expensive if new, still need to invent a way to fasten ferrite
core to spindle, screw protudes.