Yet Another Prusa Mendel Z Coupling
by nophead, published
Couples a 5mm motor shaft to an 8mm threaded rod, ensuring they are coaxial, but allowing some angular movement if the rod is not straight. See http://hydraraptor.blogspot.com/2011/06/yet-another-prusa-z-coupling.html.
Place some plastic tubing over the motor shaft and then clamp it with M3x20 bolts. Make sure there is no grease on the motor shaft by wiping with alcohol.