Park Tool’s GSC-1 GearClean Brush is specially designed to free your bicycle drivetrain from muck and grime. A comfortable handle with a curved, toothed end reaches dirt deep between the gears, and tough nylon bristles clean the derailleur and chain. Saves wear and tear on your chain and cassette. Also works great on brakes or other places where dirt collects.ush, with tough nylon bristles and a curved toothed pick to clean grit and grime from gears and small components