Isonoe footers have ball bearing feet, what keeps them from rolling off the platform?

As noted in the title...   If I don't use the optional rubber feet, either with or without the glass inserts, what keeps the turntable from not rolling around or even worse onto the floor?  I plan on using on a SL1210.  
Thanks, John
Isonoe footers, I just had a look and it appears the bearings are sitting in a recess in the bottom of the isolater. That indent I would presume would limit the ability for them to roll very far. A photo of underneath should clarify the answer to your question.
With those feet isonoe offering optional sorbothane/glass pads, but i don’t use them. You can try and later you can add those sobrothane pads if you wish.