Thanks Graham:) I've never cut a long metal screw to length before. Do you use a hack saw? How do you make sure the threads at the newly cut end will still thread into a brass nut? As in not damaging the threads when I cut it to length:)
Hacksaw works fine. File off the burrs.
Brass is pretty soft. and threads can be "pushed back" to the correct shape by turning a suitably threaded steel nut over the squiggly thread. when cutting off a piece, always leave one end with good thread, so you can turn the steel nut onto the tube.
I got a 22" wooden disc to go with it. Can I use that size of disc for a 20" diameter shade and smaller?
Yep, 22" is fine.