Summary video: http://www.youtube.com/watch?v=Bc-pEWRrJsc&feature=youtu.be this coupler will compensate small or lages align errors between z treaded rods and motor shaft, the middle piece will do it by moving itself, if the rod is out of centre of 5mm will work too!! soon a photo of printed item :) if the print head touch the printbed after a few turns the coupler will not pull the rod because it will disassembly, is a sort of z-saver, but i i have design another version for upside motors wich block this feature Instructions print all 3 files 5mm, 8mm and middle part to get one coupler, adjust it if needed with sharp to make all parts fit and slide togheter, i have leaved holes for small 2.5mm wood screw if your prited part is not too strong or simply you need more affidability, add grease in the spaces between each parts and mount it