1964-72 , W-30, , W-31, 350, Hurst Olds, F-85 Harmonic Balancer Bolt and Thick Washer. This is the bolt that threads into the end of the crank and holds the balancer on for all -350--455. The old ones are usually rusted and pitted. Thee are high quality, exact copy of the originals, they have the head marking U with 5 dashes in the same material as the originals and plated black.