Rethreading dies - pipe threads

[Wicsteve]

I'm curious about the difference between a thread cutting die (pipe thread) and a rethreading die. A rethreading die is suppose to prevent the die from removing material and prevent the cutting of a new thread path ... but how does it do this?

 

[SMOKEY44211]

A rethreading die is rounded where the cutting edge of a threading die would be. Most bolt manufacturers use this method to "roll" the material to shape rather then cut it. Denser stronger thread is the result.-----Phil