The face of the crankshaft pulley where the ratchet nut engages should protrude beyond the edge of the crankshaft. If it doesn't, the ratchet nut will never tighten the pulley. This is normally caused by improperly machined crankshaft pulleys/crankshafts. This shim washer will accommodate these problems and allow the pulley to tighten. The pulleys we sell are machined to the Ford specifications and will not require this shim.