So I'm looking around locally for tumbling media and some of the information I'm getting is kind of confusing/ hard to interpret. So far I've got the Lyman red Tufnut, and green corncob media. I want something more abrasive though, that will remove fine scratches or light rust. I've seen these in stores:

Walnut Shell #18-40

Abrasive bead glass #50-80, and looks like it says 150-280UM, the letters are hard to make out but the numbers are for sure.

Aluminum oxide #80

Crushed glass 20-30

I take it the crushed glass would be too harsh, but what about the aluminum oxide and bead glass? What do the numbers mean? Some type of grit rating?