The smooth rods are offset from the lead screws ... It seems plausible that it could be a more dominant factor in accuracy than the pitch accuracy of a hardware-store threaded rod vs. an acme screw.

It’s also found in lead screws such as those used in linear actuators ... A very common standard in the building industry but not common for machinery. Threaded rod is often Whitworth ...

Ok, I lied. This is more of a "do my math" request than a question. :p I'm working on a project that requires lifting a 10 lb load vertically using a lead screw (threaded shaft) and then lowering ...