How to apply a ball joint to ROTF Primes head
 

Hello again fellow arkers!Can I ask a question?How do customizers apply a ball jointed head to the head of ROTF Leader Prime?I've seen Encline do it, I saw alot of customizers do it, even fellow arker/customizer sabretoothe. And what are the materials needed to make that head move all the way around? Anybody who can answer this, I owe them a debt of gratitude. Thanks! :)

Take a look at Jin Saotome´s page on the subject, I think it is the same principle.
How to add a ball joint neck to a Transformers Figure

Thanks!