These dampers are specially tuned by GM engineering for up to 9000 RPM usage. They are used on all small-block V8 engines with standard size crankshaft hub diameter.These dampers employ 70 durometer O-rings to dampen harmful crankshaft vibrations. The black outer ring is fully degreed with contrasting white marks to simplify ignition timing and valve lash adjustments. The hub is drilled and tapped for standard pulleys and accessory drives. The dampers are the same as P/N 7.74" in diameter and weigh 8.95 pounds.