The first version Marcus made was just the balls. From what I understand there was not enough drive out of it, diff'd too much probably.
Version 2 introduced small pins that sit next to the balls to lock it in a bit more. You can add or remove pins depending on what kind of diff action you want out of it.
Ross (gone to scte) made one and I don't think he was ever really happy with it.
You need the pins and a very large expensive machine to do it with.

Take a look at rcshox site and you can see pics of the spur and the machining needed.