A system and method for automating an assembly process of threading a tube-nut onto a threaded connector. The system includes a robot having a force sensor and a tube-nut runner tool coupled to the robot and having a tool head with a rotatable socket therein. The method includes engaging the socket to the tube-nut under force control using the force signal from the force sensor. The tool controller causes the socket to rotate the tube-nut where the tool controller controls the torque and/or angle displacement of the tool head to tighten the tube-nut on the threaded connector. The method also includes disengaging the tool head from the tube-nut after the tube-nut is properly tightened onto the threaded connector under force control to ensure that the end member is properly disengaged from the tube-nut.