Head Stud Thread

[Parazine]

I've never understood the purpose of a die nut. If a die needs to be adjustable (and they all are) then how can a die nut ever be right?

They're actually quite useful, where a thread needs to be cleaned up as opposed to cut from the start on a piece of rod. They can also be driven with a socket rather than a die holder, which improves accessibility.
Like Tony, I try to find reliable old brand die nuts, the Chinese type are too unreliable.