Ah the elusive magic ball, I remember one of the guys I worked with had a whole bag of them, so he was like the magic ball dealer. Then one day I saw bean bag break open and shazam, it was filled with the magic plastic balls. What am I talking about? The bumper between the contact screw and contact binder screw. If you were to run that steel screw into a soft metal like silver or copper it will damage the threads so you need a little plastic bead to bumper it.
Over the years I found that those hard plastic beads can actually damage the threads as well, so I moved to cutting up O-rings and using the rubber pieces. It locks in the contact screw and doesn't cause as much damage to the threads.
I just take a regular O-ring, cut it into pieces and slide it right into the contact binder.
Screw in the contact screw binder until it's snug and you should be good to go. That's it, no special ball needed. I know somewhere a supplier has a warehouse full of cut open bean bags that is going to be mad at me. If you are in need of the magic O-rings, we do sell them.