In a method for manufacturing a rotor hub for use in a spindle motor, free-cutting stainless steel is used as a material of the rotor hub. A slug of free-cutting stainless steel is subjected to a plastic working to form a disk mounting portion and a cylindrical surface positioned radially inwardly of the disk mounting portion. Then, a cylindrical disk fitting surface is formed by machining substantially the entirety of the cylindrical surface. The rotor hub contains A-type inclusions appearing in a cross section taken along a center axis of the disk mounting portion. The A-type inclusions are oriented in directions different than the center axis.