I've had good luck with the 6" pads and sticks from H-D on all kinds of metal. If your just starting, read and try a few different compounds and you'll get a feel for what works for you. At first i just grabbed any thing metal i could find and played with it. It's actually pretty cool the results you'll come up with. I polished my 25 yr. old wedding band and it looked better then the day i bought it....lol.
I should add that keeping the wheel clean is most important. Just take a flat blade screwdriver to the wheel every now and then and you'll be good.
