I love mics, really  all precision measuring stuff.  These are easy to collect,
small ( a bunch fit  in a shoe box), actually do something (moving parts to play
with) and are just one more slippery slope to slide down.  Anybody need one, let
me know, yours for the price of postage.  I'm about to join a mic 12 step
program, if I can find a local chapter.
Yes, the threaded thingy inside is a 40 pitch, so 1 turn is 25 thou.  
Yes, the only necessary adjustment is to set 0 when the anvils make contact
using the ratchet.  Don't crank down using the sleeve, this is a light touch
tool.  Keep the faces clean.
While we're on the subject, NEVER, EVER put a mic away with the spindle and
anvil in contact.  Temperature changes could damage the mic.  A wipe with a rag
with a very light weight oil is good protection from corrosion.
Even hand body temperture affects the frame, the reason for the plastic
insulation on some models.  Others use a tubular frame.  The frame ridges on the
classic Starrett 436 are partly as temperature compensation, if the temperature
goes up the whole thing expands, but the outside of the frame expands more,
pushes the anvil back in.
And yes, the lines on the rotating sleeve are classic vernier scale, find the
one line on the sleeve that lines up with the non-rotating part, read that line
as "tenths".
The 1" standards are to set the zero for 1" - 2" mics.  
Zeroing needs doing from time to time. It is a friction lock of the
spindle/screw and the spindle.   Think of putting two washers on a bolt.  They
can still slip.  Calibration, checking the accuracy full scale, is an annual
thing, and should be a direct result of the thread pitch.  If it ain't right not
much you can do, toss it, unless it is a backlash issue, or simply not zeroed.
There are some ingenious methods to take out almost all backlash.  
Calipers are a bigger problem to keep true, as the rack and pinion setup is
suseptable to particles, broken teeth, crud, and the rack is exposed.  We call
them guess-o-meters.

The ball style anvil can be used on curved surfaces, like the wall thickness of
a tube, as long as the radius of the tube is larger than the ball's.  (Woundn't
be able to get the mic in there if it wasn't)  They also make "tube mics", where
the anvil part of the frame is a rod of about 1/4".

A lot of guys keep a second set of mics around as "loaners", cheap on ebay, and
if some gorilla cranks on the sleeve it ain't the end of the world.



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