Safe, cheap and effective. You can find it in grocery stores, automotive stores and who knows where else.
It works best if its hot but works pretty good at room temperature.
For bare steel, you should dry the part and oil it afterwards. Think of it as good detergent.
Don't soak high strength aluminum parts in it for long periods of time, it very slowly eats them away. No problem with cleaning aluminum parts if you rinse them off afterwards.