I clean screws and small parts in a tumbler. It’s a rock tumbler. Wish I had an bigger one for row locks and larger parts, but....
First I clean them with paint remover or acetone. I do that in a varnish can that fits on my tumbler.
After rinsing, I put the parts in a rubber drum with treated walnut shell media and let them tumble a couple of days.
Bits of the walnut get caught in the screw slots, but they are easily removed.
I bought the tumbler from Harbor Freight and get the media on eBay. It’s normally used for polishing bullet casings.