This coupling is used for connecting motors to lead screw on Prusa Mendel and other 3D printer / CNC machines.
Specifications:
Material: Aluminum
Couples 5mm shaft- 8mm shaft
Length: 25mm (.98")
Outer Diameter: 20mm (.79")
Please note that the diameter of threaded rods may be slightly less than 8mm. So, in order to get a close fit with the coupler, wrap the end of lead screw with thread.