Yet another Z Shaft Coupler for Prusa Mendel

I bought motors that happened to have rather short shafts, and 2 flats cut at 90° to each other, and was having a lot of trouble getting the standard couplers to center and hang on to them, so I decided to design my own.

These use trapped nuts and grub screws to hang on to the shaft - one pushing the motor shaft into the flats on the motor shaft hole, and 3 holding the z axis screw.