In the manufacturing process of the corrugated holder, the press-in portions 24 (24a, 24b) formed at the proximal ends of the truncated portions 13b, 13b of the rivets 9b, 9b are inserted into the respective through holes 12a, 12a of the one retainer element 8a, , 24 are press-fitted into the intermediate assembly 17a, and the intermediate assembly 17a is nitrided. The axial dimension X of each of the press-fitting portions 24 and 24 is smaller than the axial dimension Y of the through-holes 12a and 12a (X Y). As a result, portions that are not in close contact with each other are formed in a part of the axial direction of the inner peripheral surface of each of the through holes 12a and 12a and the outer peripheral surface of each of the intersections 13b and 13b, and a nitrided layer is formed .
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