This is a parametric Z rod/motor coupler for any 3D printer. Originally made for the Bukobot 3D Printer ( http://www.thingiverse.com/thing:21746 )
Features a "Flex Chamber" to be a little flexible for the not-so-straight Z threaded rods and one piece for both sides.
I included two popular sizes:
8mm rod to 5mm motor
6mm rod to 5mm motor
OpenSCAD has all the variable to adjust to your needs.
Try to print with heavy fill for it to be strong.