It's the RepRap extruder drive screw which fits in the bearings shown in my last post. The RepRap instructions say to use a blow torch and plumber's flux to attach the steel cable but I found it easier to use a soldering iron and electrical solder.
Here it is installed with a small G-clamp in place of the top half of the pump :-
And here is a video of it being tested with a variable DC power supply until it shed the clamp :-
