Vinegar works very well on small parts. BTDT a few hundred times. Cheap too.

Simple steps:

1. Remove all grease and loose rust with dish soap and tooth brush.
2. Immerse in vinegar. Check progress each half day or so. If part still not clean but rust can be scraped off with a knife, do so. Re-immerse. Remove when clean, a few days. Phosphated parts take a little more time to strip off the old phosphating (ignore the stink).
3. Hand wire brush all over wearing gloves. Never touch a clean part with bare fingers.
4. When part is clean and wire brushed with no fingerprints, it is ready for re-paint, re-plate, or re-phosphate. Parts that have been wire brushed will not re-rust for a few weeks or months if kept indoors in air conditioning.

Photos show parts after wire brushing. Only fasteners are shown, but this process works on other small parts just as well.