Base member, spindle motor including base member, hard disk drive device, and method for manufacturing base member

A base member, comprising:

• a plurality of combinations of a projection and a component placement part, the projection having a cylindrical shape and projecting in an axial direction,
• wherein
• the projection and the component placement part are adjacent to each other via a curved surface part having a first curved surface and a second curved surface,
• the first curved surface and the second curved surface have a diameter increasing toward the component placement part in the axial direction,
• the second curved surface is located closer to a side of the component placement part than the first curved surface in the axial direction
• the first curved surface is continuous with the second curved surface in the axial direction and in a radial direction,
• the combinations of the projection and the component placement part having the substantially same dimension in the axial direction, and
• a difference between a maximum value in the plurality of combinations and a minimum value in the plurality of combinations of a height in the axial direction of a boundary surface between the component placement part and the second curved surface is smaller than a difference between a maximum value in the plurality of combinations and a minimum value in the plurality of combinations of a height in the axial direction of a boundary surface between an outer peripheral surface of the projection and the first curved surface.