Low Cost Z Axis Coupler for Prusa i3 and other 3D printers

This thing is simplified shaft coupler designed for 3D printers. 3D Printing applications do not require lots of torque to drive Z axis. Rigid construction works fine if your 3D printer is relatively straight and right.
Please see instructions on how to make this thing, or buy ready made couplers:
5 to 5 mm
http://www.ebay.com/itm/-/221611355801
5 to 8 mm
http://www.ebay.com/itm/321498700056