I keep this Nut and Bolt NE of Barry's bookmarked:

http://moi3d.com/forum/index.php?webtag=MOI&msg=9949.1

Yes, very useful.

What I wanted to model was a long, LH thread leadscrew. I made a long (300mm) Cap Head screw. Cut the head off and mirrored the resulting threaded rod. Although its a set of joined surfaces rather than a solid it meets my immediate needs.

Thanks again Barry.