| 摘要 |
While one end of a material (31) that has nearly the same diameter as that of a first connecting portion (15) is secured, pressure is applied to the portion between the middle and the other end of the material (31). A slender portion (32), which has nearly the same diameter as that of a buckle portion (18), is formed adjacent to said other end of the material (31), and a stepped portion (20) is formed adjacent to the slender portion (32). Thus, a first-stage unfinished body (33) is formed. By radially enlarging a part of the slender portion (32), i.e. the portion between the distal end and the portion to become a buckle portion (18), until the diameter of said part becomes nearly the same as the diameter of a second connecting portion (16), the portion to become the second connecting portion (16) is formed. Thus, an arm-to-be portion is formed, wherein the portion that has not been enlarged shall be formed into the buckle portion (18). With external threads (17) formed along the cylindrical outer surface of the expanded portion, formation of the arm (5) is completed. The invention enables the reliable formation of a buckle portion (18) having a given length, resulting in stable production of arms (5) having a uniform buckling strength. The invention enables the easy production of an arm (5) regardless of whether the two ends of the arm (5) have different diameters.
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