Very nice original design. This eliminated most of the wobble induced by the original couplers that I never could centre properly. However the 8mm top threads were too tall for my printer since I have a Z Wobble thing attached. So had to cut both the coupler and the 8mm nut to decrease the height. Works great now.
The 5mm nut is from the original great design.
Geeetech Full Metal Aluminum
The original part tended to break at the joint so increased the infill to 100% to make it as strong as possible. Printed in PLA.
Used netfabb Basic to slice the 8mm nut and the main coupler in the 8mm section.