Joint I designed that eliminates nonlinearities in motor shaft and threaded rod. My prints had improved since I use it.On the last picture - left one is after attaching joints and right one before.To mount on motor (5mm shaft) use 1 M3 nut and bolt, for threaded rod just screw it into the piece. The cross part that connectes them is not yet finished. The most final concept is to connect it with small parts of 3mm filament which is pretty good for now.I almost forgot - I use only one M8 nut in each XEnd and no Z rod constrains so the threaded rod can woble and I think it's much better way when the geometry of printer isn't perfect which is difficult to achive in Prusa.