I'm toying with the idea of designing my own 3-axis milling machine and to that end I was looking at some ball screw kits and and noticed a lot of them come with the 'BK' style bearing mounts. I understand that they're used to prevent axial forces being transmitted to the stepper motor during operation, but I can't get my head around how they achieve this with the way they're designed. Could someone please explain how they work?