The Park Tool CM-5.3 Cyclone Chain Scrubber is a professional-grade shop tool engineered to deep-clean bicycle chains quickly and effectively without the hassle of removing the chain from the bike. It works by clamping directly around your chain, utilizing a system of internal rotating bristles and solvent to strip away built-up grit and abrasive factory grease.
The CM-5.3 is widely reviewed as the gold standard for on-the-bike chain maintenance.