Shaft is a mechanical part that normally has a circular cross-section. It is used to Transmit Power Through Rotation. It provides an axis of rotation for a variety of mechanical components fastened to it such as Sprockets, Gears, Pulleys, Flywheels & Cams. It is used to Control the Geometry of their motion while they are rotating.
A threaded rod, also known as a Stud is a relatively long rod that is Threaded on Both Ends; the thread may extend along the complete length of the rod. They are designed to be used in tension. There are basically three Types of Stud, Fully Threaded Stud, Tap End Stud & Double End Stud.