Today I have a tool tip. When I need to clean rust or crud from parts this is what I reach for. This is a wire brush that is made for cleaning the inside of copper pipe fittings before soldering them. You can find them in a few sizes in the plumbing section of any hardware store. They have very stiff bristles that scrub well and they also fit into holes and small spaces.
I also have a few that I have cut the handles off. If you put them in a drill they make parts cleaning fast and easy. The photo shows the end of an axle that I cleaned using one of these brushes.