Atlas made the lathes for Craftsman and at the very end, I believe Clausing was involved. They are very capable machines and very easy to fix.
A lot of chucks were flat backed with no mounting system and would bolt onto a plate designed for a specific spindle nose such as D1-3, 1 1/2-8 threaded, or L00 taper. They could make the complicated part (lathe chuck) in one SKU and adapt to many lathes with the cheap, changable backing plates. Smart design.