I have been doing some research on this and came across this posting.
http://groups.google.ca/group/rec.crafts.metalworking/tree/browse_frm/month/1993-09?_done=%2Fgroup%2Frec.crafts.metalworking%2Fbrowse_frm%2Fmonth%2F1993-09%3Ffwc%3D1%26&fwc=1