The Z axis rod that came with my QU-BD Oneup kit had the hole drilled off center and not inline with the rod.
This caused the entire extruder assembly to move (not in the Z axis) as the rod spun, I did not try to print before making this change but i suspect this would cause some Z banding on the vertical sides of the print.
Also I did not like the idea of using lock tight to mount it to the motor.
I used a little hot glue but it was made to be a tight fit so you could get away with not using any.
A added advantage, if you do not glue the coupler to the stepper motor the coupling will force itself off the motor if the Z axis is lowered to far, minimizing damage. Ask me how i know:D
5-7-14 Added requested coupler for motors with no flat ground in the shaft, reduced diameter by .07mm. No guarantee that it will not slip on the shaft.