This "Self Centering Zip Tie Coupling" works very well for me.
My wobbles are gone now.
Just stick it on the motor shaft, put the threaded rod inside and tie it with 2 zip-ties.
Printed with 100% infill.
It's 5x5 and 5x8 Version.
The coupling ist mounted since 02.04.2017 and it's still working very well (08.01.2018).