Thread rolling machine - GIF

[JoeVanGeaux]

So why doesn't the screw screw in as it is being formed?

Ralph

I thought the same thing, but when I looked closer at the relative rotations between the screw(bolt) and the dies, it looks like the bolt is unscrewing itself backwards at the same rate that the dies appear to be drawing it forward. (Basically, a different way of saying the same thing as what IAMSatisfied, said.)