JPG gave you the catalog link. It is the Universal 5/8" Arbor now known as the Molder/Dado Arbor. Yours looks like the second version of four. The name changed while the third version was in production but the part number has always been 505506. In the picture below are the four versions on the bottom row.
Mark V completely upgraded to Mark 7
Mark V 520
All SPT's & 2 Power Stations
Model 10ER S/N R64000 first one I restored on bench w/ metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ metal ends & retractable casters.