without posting a picture i will try to describe and maybe someone will be in the know. . .
its called a GLENCO floating holder. mfg. by j.c.glenzer in detroit. it sez 613-s on the top of the input shaft that would go into a mill or something and its input shaft is 1" diameter with a flat spot on the side of it.
the output is about 3/16", using a split collet with a setscrew to hold the 3/16" thing (whatever would be put into the collet). there is a rod in it now thats just there, loose.
hummmm ! enuf information without trying to take a pix of the dang thing ?
it came with my craftsman / atlas but im certain its not part of it.
davidh (the old guy)