To achieve a structure with which a stud 9a can be easily inserted into and extracted from a mounting hole 17 in a mounting flange 7 in a rolling bearing unit 1a for wheel support which keeps pitch circle diameters of outside-row balls 4a, 4a longer than those of inside-row balls 4b, 4b.

Each stud 9a forces an outward flange-shaped collar part 19a formed in each base end thereof abutted on an axial inside surface of the mounting flange 7. Each intermediate part or tip is fixed to the mounting flange 7 in a state of projecting from an axial outside surface of the mounting flange 7. The shape of the collar part 19a with respect to an axial direction of each stud 9a is a non-circular shape in which one part of an outer diameter is smaller than the other part thereof. At the insertion and extraction work, one part is situated in a radial inside of the mounting flange 7, so that the interference between the collar part 19a and outer peripheral edge of a joint flange provided to an outer peripheral surface of an outer ring 3 is prevented.