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 partsPrint the v4 coupler, then print a 5/16 nutcap. Put a piece of tape over the shaft hole of the coupler (or insert the stepper motor). Squirt some silicone into the coupler and set the nutcap in the hexhole. Let set-up as directed on the tube of silicone. Insert m4 nut, then m4 set screw to coupler. Then put 2 nuts on the end of your threaded rod, tightened against eachother. Use a 608 bearing holder if you have a prusa, my printrbot has gravity on it's side.SCAD file only work in the prusa folder, unless you change out the variables