Fastening structure including a bolt having a serration that is press-fit into a bolthole of a flange

A device for a wheel, said device comprising:

• a bolt having a bolt head, a larger outer diameter portion extending in an axial direction of the bolt, and a smaller outer diameter portion extending in the axial direction of the bolt and provided with a thread portion;
• an inner ring member having a flange portion in which a bolthole is formed and to which a brake disk is fixed by the bolt passing through the bolthole of the flange portion and a hole of the brake disk, an abutting surface of the bolt head abutting on a seat surface of the flange portion of the inner ring member;
• an outer ring;
• and
• a plurality of rolling elements disposed between the inner ring member and the outer ring,
• wherein an outer peripheral surface of the larger outer diameter portion of the bolt is provided with an engaging portion engaging with the bolthole of the flange portion,
• wherein a length of the engaging portion is shorter in an axial direction of the bolt than a thickness of the flange portion, and
• wherein a center portion in the axial direction of the engaging portion coincides with a center portion in the axial direction of the flange portion.