The basic function of all couplings is to transmit power, accommodate misalignment and compensate for axial movement (end movement of shafts). Sometimes, a coupling is asked to absorb shock or vibration. Selecting the right coupling depends on four basic conditions of shaft misalignment or movement.
Parallel misalignment occurs when the two shafts do not share the same rotation axis. Their end faces may be parallel, but their center axes are laterally displaced with respect to each other.
Angular misalignment applies when shafts are neither coaxial nor parallel. The angle at which the shafts are misaligned may be symmetrical or asymmetrical.
End float occurs when either or both shafts display axial movement, moving in and out. A sleeve-bearing motor, for example, "floats" as the rotor hunts for the magnetic center of the winding. Temperature variation can also cause thermal expansion and variation in position of the shafts.
Torsional flexibility is the torsional movement in planes perpendicular to the shaft axis. Shock or vibration typically causes this. A torsionally flexible coupling absorbs and dampens these movements.

The basic function of all couplings is to transmit power, accommodate misalignment and compensate for axial movement (end movement of shafts). Sometimes, a coupling is asked to absorb shock or vibration. Selecting the right coupling depends on four basic conditions of shaft misalignment or movement.
Parallel misalignment occurs when the two shafts do not share the same rotation axis. Their end faces may be parallel, but their center axes are laterally displaced with respect to each other.
Angular misalignment applies when shafts are neither coaxial nor parallel. The angle at which the shafts are misaligned may be symmetrical or asymmetrical.
End float occurs when either or both shafts display axial movement, moving in and out. A sleeve-bearing motor, for example, "floats" as the rotor hunts for the magnetic center of the winding. Temperature variation can also cause thermal expansion and variation in position of the shafts.
Torsional flexibility is the torsional movement in planes perpendicular to the shaft axis. Shock or vibration typically causes this. A torsionally flexible coupling absorbs and dampens these movements.