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Thread rolling cylindrical dies.
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Previously:
https://www.homemadetools.net/forum/...3730#post99885
https://www.homemadetools.net/forum/...718#post139938
Seeing as to how rounded the root of the thread was when completed this looked a lot like a short ball screw spindle possibly even to eventually become a steering gear shaft.
Edit"" after viewing the gif again I am convinced that is what it most likely is you can see a splined end at the beginning in the lower part of the frames plus a bearing or more likely the seal surface is being rolled there during the threading operation.