How much weight can a 3/4" black iron pipe support hanging from its threads?

snipped-for-privacy@aaronj.com (Stu)

I don't know what the engineers will say, but I think you have too many unstated variables to get a meaningful answer. The pipe itself is mild steel (common name, "black iron'). What's the flange made of? Is it of the common cast iron sort? What ceiling material is the apparatus being screwed into? What material and dimension are the screws? Is it for dead or live loads? My suspicion is that you'd have failure of some component other than the screw threads first. The components you're using are not intended as a form of hanging-load fastening system. Perhaps it would be better to consider some other form of load carrier, such as some methold of tying into the joists (rather than merely "ceiling") above.

On the other hand, I've seen some heavy cast iron stuff lag screwed into joists in older machinery transmission, for ex, the hangers for lineshafting and countershafting. Frank Morrison.

Cast steel from HD

The pipe goes through 2 layers of 3/4 plywood and is then screwed into an upside down floor flange.

Thanks,

Stu