MULTI-PITCH SCREW AND METHOD AND DEVICE FOR MANUFACTURING THE SAME

PROBLEM TO BE SOLVED: To provide a method of easily manufacturing a multi-pitch screw with a thread rolling flat die suitable for mass-production.

SOLUTION: The thread rolling flat die 4 comprises linear coarse threads 40a and multi-pitch threads 40b continued to the coarse threads 40a, slightly lower in height than the coarse threads 40a, having both side walls formed so that districts of the threads apart from the centerline 40c of the threads and districts close to the centerline are alternately continued along the centerline 40c and can be symmetrical with respect to the centerline 40c of the threads. Since the locus of the multi-pitch screw by the multi-pitch threads 40b after the locus of a fixed lead angle is formed on the outer peripheral surface of a shaft-like blank material by the coarse threads 40a, the locus of the multi-pitch screw enabling a force applied thereto in rolling to be changed can be easily formed.

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