You can't feel them or hear them, but harmonic vibrations are at work inside EVERY internal combustion engine. That's not good. Similar to glass-shattering forces created by a high pitched note, harmonic vibrations cause metal fatigue and can cause significant power loss because crankshaft harmonics are transmitted to the camshaft and valvetrain. Control this power-robbing force with a Fluidampr harmonic damper that uses race proven vibration damping technology. A high viscosity silicone fluid surrounds a nylon-coated inertia ring inside a laser welded housing. All dampers are coated with a black zinc chromate finish for increased corrosion resistance. Timing marks - every two degrees from 50 degrees BTDC to 10 degrees ATDC with additional marks at 90, 180 and 270. Meets SFI 18.1 specs. Made In The USA.