Interesting old tool holder

I have puzzled over these in the past.    The first one came in a lot of tool holders for the Sidney.  The atlas came with one too but smaller of course.

While trying to enlarge a .6 something hole to .6686 I was forced to look at the tiny boring bars that came with the atlas.  Rods really.  Then while wondering how to hold them I recalled this tool holder.   The real give a way is the screw pushes the tool down into a V.   

Need to get some better images.