Bill Noble wrote:
here's the link
http://cgi.ebay.com/ws/eBayISAPI.dll...m=300462460475

I was able to find the manual page for this on line, so that link is on
the auction page - very nice, very huge - I wonder what its original
application was - anyone got a Mitutoyo catalog from about 1980? Can you
look up 252-372 micrometer head and tell me what it was supposed to be
used for? Just curious.

I've seen micrometer heads nearly this big on
chambers of scanning electron microscopes.

They are used to move the internal stage.