Prusa / Printrbot generic z axis coupler

coupler that works with 5mm stepper motors, when the 5/16 threaded rod is double nutted. Hex hole is slightly bigger than a 5/16 nut, re-print hole bigger and fill with silicone if backlash is an issue for you.
Now with new version 3 that has two setscrews, Version 4 is two parts