This is one of the FAQs that appears to have been deleted in the transfer to the new forum. (my BROWSER) remembers some of these FAQ entry titles, so that's how I know).
So as a bare bones, 1997 had an HSS design specification (editorial comment: that was to some degree, ignored). This is where the design thickness change first appeared. Later on, the changes were rolled into the 2005 specification.
Specifying HSS, Stein, Modern Steel Construction, July 2005.
