Polishing a Micro Seiki RT 3000G Gunmetal platter

@carlsbad2 is right on.  Stopping at 3k will probably give it a very nice finish, but if you want it even shinier, I'd end with a metal polish.

I may have misinterpreted the question.  but looks like you're getting a variety of anwers.  Good luck. --Jerry

Well, the OP didn't say what condition the platter is in, so it's hard to know what it needs.  What you recommended is on point if the platter is a little more worn than just lightly oxidized.