The SureServo™ motors have keyless shafts that are designed for use with
clamp-on or compression style couplings. Couplings using keys and/or set screws
should NOT be used with SureServo™ motors as they are likely to come loose or
damage the motor shaft. "Servo grade" clamp-on or compression style couplings
are usually the best choice when you consider the stiffness, torque rating, and
inertia.

Higher stiffness (lb-in/radian) is needed for better response but there is a
trade-off between the stiffness and the added inertia of the coupling. Concerning
the torque rating of the coupling, use a safety factor of 1.3 to 1.5 over the
SureServo peak torque requirement of your application.