I needed a way to connect my stepper motor to ACME rod, so I figured that if I'm going to print one, I might as well see how well a helical coupling prints. It came out better than expected, but I can't claim anything about performance or longevity of the part.I didn't model this in OpenSCAD, so I have also included my Alibre Design 2011 part. If you need a specific motor shaft or rod diameter, just send me a message and I'll upload a file for you.