STFU BIKE TRAIL (FITS UP TO 12SPD)"STFU drivetrain damping devices are designed to keep your bike running quiet and efficient while minimizing wear. Includes two adjustable modules that mount to your swing arm. Dual compound hard plastic insert keeps the unit stiff and in place with soft over mold for sound damping. Suits Trail Bikes with 1X gearing 9 13 speed with up to a 52 tooth cassette Trim to length, fits most bikes Light weight and silent"