Park Tool, GSC-1, Gear clean brush

The GSC-1 is specially designed to free your bicycle drivetrain from muck and grime. The comfortable handle features tough bristles clean the derailleur and cassette, and a contoured toothed end to reach dirt deep between the gears. Saves wear and tear on your chain and cassette. Also works great on derailleur pulleys, brakes, or other places where dirt collects.