Hi kb, check out these previous discussions for how to model threading:

http://moi3d.com/forum/index.php?webtag=MOI&msg=767.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=490.36
http://moi3d.com/forum/index.php?webtag=MOI&msg=2133.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=2226.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=3217.1

And also a plug-in here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5451.40

- Michael