The PS20F is necessary to use any 5th Axis 96mm system. The 96mm spacing on 5th Axis vises and adapters allow for compatibility with other competitive systems (Lang, Gerardi, Schunk, Gressel, Jergens). *Please note that pull studs must stay with the corresponding companies base plate.
The spacing and thread allows for the top tooling to be interchangeable between the systems. If you are using a 5th axis RockLock base plate you will need 5th Axis pull studs (PS20F). If you are using a competitors base plate you will need that companies pull studs, all of the top tooling (vises, fixtures, etc.) is interchangeable.