There's all-thread, and threaded rod. All-thread comes from the hardware store, and it's junk. Not made of the same material twice in a day, and load capacity all over the map.
Threaded rod is the stuff listed by Grinnell and others specifically for supporting pipe and equipment. Like Satchmo says, it's in any reputable support manufacturer's catalog. It will have ASTM grades listed along with capacity data.