BK Style Bearing Blocks for Ball Screws

[Machinery Jones]

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?

[Muzzer]

This gives a good explanation.
https://www.thk.com/jp/en/products/b.../support_unit/

I typed a reply but got a "bad gateway" when I tried to post. I usually copy the message before trying to post, just in case - but Sod's Law. Doh!

BK is a fixed brg that takes radial and axial thrust, whereas BF only provides radial support. If the ballscrew expands or contracts, no stress is imparted to the ballscrew or machine frame. The stepper is next to the BK so that there is no thrust on it.