Are there any particular types of stainless steel that take on a good
shine and keep it better than others? Rod form of about 3/4" is what I'd
use. There will be an external and internal threads with one end of the
rod being visible.

The part I'm considering making is mostly cosmetic, but having an almost
chromed look is a plus. The polish I have on hand is Blue Magic, and the
while the stuff is great, but I've noticed that even with stainless
silverware not all will even take a nice polish. Some stuff just ends up
looking grey, others will really shine. I realize "stainless" is a loose
term and the properties vary quite a bit.