[rackops]

I've tried everything that I can buy locally, and the best I've ever used is gasoline.

Yes, I know, it's dangerous and has all sorts of other bad things (used to be a fuels safety officer in the military). But, it works really well. A little goes a long way and it can be used many times before it's no longer usable.

Using an old toothbrush and a mason jar of gas, along with a sacrificial baking dish, you can easily remove all the gunk off many nuts and bolts. Follow up with a good degreaser to remove the gasoline residue once clean.

Always wear PPE. Don't smoke while cleaning parts. Don't use the mason jar for food. Don't use the toothbrush for brushing teeth. Don't bake anything in the baking dish. Don't get it on your skin or in your eyes. Always properly dispose of any unusuable product. Don't allow it to atomize. Don't eat afterward until properly washing. Don't drink it. Don't wear good clothes. And other common-sense things as caveats.