High quality couplings are often made from Aluminium. Different types exist.
(please insert examples with pictures)
In several cases a sort of plastic tube have been used as a coupling between the motor shaft and the threaded rod.
- aquarium tubing
- silicone tubing 4mm inner diam. - 6mm outer diam.
- polyurethane tubing
- heatshrink tubing 3:1 ratio (12mm to 4mm) with adhesive
- vinyl end cap from hobby rc cars 4mm inner diam. - 10mm outer diam. - 22mm long
As mentioned in this thread : http://forums.reprap.org/read.php?283,151801,151801