The swivel head of a driving spindle of a four-high mill fractured. The fracture originated in a darkly stained spot on the bottom of the cylindrical part and then continued into the cylinder walls in the two directions. The fracture topography was of dendritic structure at the stained spot. This led to the conclusion that a shrinkage cavity was present. Metallographic examination confirmed that the fracture of the swivel head was caused or favored by a cavity.