Not a nail set...it could be used for that purpose if it were a big nail. And YT I suppose it could be used to "ream" something out. But that is not it's designed purpose.
My guess is that it's a pin that holds two things together. The taper helps align the holes and those "dots" are small holes for a retaining clip to go through.
This one is old, and has pretty much seen it's day! I use this one for a punch of sorts sometimes. Yes, newer more modern ones are still used, and needed!!!