Abstract: A spindle motor for a disk drive includes a shaft, an aluminum hub, a bearing, a magnetic steel back iron, and a magnet. The hub includes an axial wall having an inner surface. The back iron has an upper portion and a lower portion. The hub is concentrically position about the shaft such that the inner surface extends along a direction of a longitudinal axis defined by the hub. The bearing is positioned between the hub and the shaft. The back iron is secured to the hub such that the upper portion abuts the inner surface, whereas the lower portion is spaced-apart radially from the inner surface, thereby forming a single gap between the back iron and the hub. Finally, the magnet is attached to the back iron such that an axial length of the magnet is substantially coextensive with an axial length of the back iron.