Rusty fasteners get a bath in muratic acid and water 50/50 mix then baking soda water to neutralize. Just be careful and follow all precautions!
Don't over do it...
I have a Thumbler's tumbler I use to polish them. It's my reloading tumbler and I use stainless steel pin media. It works well.
A little dawn dish soap, a little brass polish with water and the stainless pins. Fasteners and small parts too.
Got mine at Cabela's
Thumler's Tumbler Model B High Speed Rotary Case Tumbler 110 Volt
Barrel Inner Dimensions: 8" x 7-1/2" x 6-1/2"
Voltage: 110 Volt
Capacity: 15 lbs
Notes: The motor turns at 3000 RPM, turning the barrel at 40 RPM