US Patent 10465688 Coupling and rotor shaft for molten metal devices

A coupling has an opening and a protrusion extending downward from the opening. The protrusion has threads that are preferably positioned outside of the opening. A rotor shaft that connects to the coupling has an internal bore with threads that receives and retains the protrusion, such as by a threaded connection between the two, so the protrusion applies driving force to the shaft.