For threading steel, I use Do-Drill. It comes from Brownell's, of Montezuma, Iowa, U.S.A. It doesn't smoke or smell as bad as plumber's thread cutting oil, and leaves a good finish.
I use WD-40 on aluminum. It costs more than kerosene, but doesn't stink up the shop/house.
I use Tap-Free, Tap Magic, or Rapid Tap to thread stainless.
Tom