RepRap Mendel Z-Axiz Stepper/Threaded Rod Flex Coupling

I'm designing these couplings to replace the stock couplings that come with the RepRap Mendel Prusa. The machine is not fully built yet, so I don't know how much flex these will have. If anyone cares to try one out and comment, I would really appreciate the feedback.

In this rev I have rounded out the inside corners, in an attempt to make it easier to "Build Up" by extrusion.