Atlas used to sell tool holders for the 10"/12" and for the 6". The holders for most of the 6" held 3/16" square cutters. There were about 7 of them, 3 for turning and facing, (L.H., R.H. and straight), 2 for Cutoff (straight and R.H.) and one each for boring and ID. threading. See the 1966 Atlas catalog which should be in Downloads. I think that they were actually made by Armstrong although that has been rubbed out in the catalog photos.