I've seen manufacturer's listings for boring bars with a zero degree lead
angle. I'm curious about the applications and set-up for such a tool. It
seems to me that if used to bore to an internal shoulder, the result would
be significant chatter. So what are the advantages of a zero degree lead
over, say, a boring bar with a five degree lead angle?

Regards,
Michael

used for thru holes , less pressure on the nose of the tool , somewhat less
chatter at long overhangs

usually only seen on triangle positive inserts