What are the exact steps to push and pull the file? I am going to need that a lot because I have to do the same with ballscrews etc.
You won't be able to stretch ballscrews, the 'move face' command only does what the name suggests - it won't extend a thread.
For coupling nuts, all you need is an extruded hexagon to give an approximation of the nut, probably quicker to model it than to find one on line.
To shorten items, a simple extrude cut either long the part or across it may be enough.
Search for 'direct editing' in the help. I'll back at my desk soon and will look to add a link.