I rebuild MGB steering columns as a sideline. These columns use alloy spacers where the column bolts to the dash. These spacers are usually a pain to clean up to reuse. I've tried tumbling them with green pyramid media without satisfactory results. On a lark, I replaced the plastic media with a box of 5/16" zinc coated steel nuts, and low and behold, the nuts worked better than any media I have tried in the past. Aluminum comes out shiny and clean, kind of burnished in a couple of hours in my small HF vibratory tumbler.