Coupling members are used for connecting rotors in long rotor assemblies. One such example is a spline coupling. This coupling connects the displacements of the rotors while providing the freedom to tilt relative to each other. Another example is a torsional coupling where the coupling has certain stiffness for the relative axial rotation of the connected rotors while keeping the displacement and tilting of the rotors rigidly connected. In general, a coupling will have some combination of allowed and restricted relative motions across the two rotors. Connection between the different degrees of freedom for various types of couplings are described in the following sections.