The invention related to a spindle motor for hard disk drives with improved running accuracy where the sheet metal package or the complete stator consisting of sheet metal package and windings is encompassed by a centering casing of plastic, which is preferably applied by means of an injection molding operation. Depending on the design of the spindle motor the centering casing can be centered on the stationary shaft and/or on the outer rings/inner raceways pertaining to the sets of roolling bodies. Furthermore, a stator without centering casing is described whose sheet metal package is centered directly on the outer rings/inner raceways.