On Mon, 24 Mar 2008 19:59:37 +0000, Dave
wrote:

Just talking from an engineering point of view, I
was always taught that a bolt had a plain shank between the threads and
the head and that a screw was threaded all the way up to the head, minus
a thread.

AIUI, a bolt is intended to be held still while a nut is tightened on
to it (a bit like a stud), whereas a screw is intended to be rotated
into the nut (or casting, or whatever).

--
Frank Erskine