This "thread" reminds me, I like measuring tools and fleabay showed me
a pitch measuring machine, not complete but that is half the fun

http://www.archivist.info/cnc/screw_error/lamp_screw.php
more pictures at
http://www.collection.archivist.info/searchv13.php?searchstr=pd+pitch
Another toy I use for smaller threads is a traveling microscope
http://www.collection.archivist.info/searchv13.php?searchstr=pd+travelling

Dave Caroline
East midlands