Looking at both the Nest iFixit teardown and this Nest bezel replacement tutorial, it looks like the Nest stainless steel bezel mounts directly to the PCBs and displays inside.
The Nest bezel is able to rotate freely though (and very smoothly, I should add) while the components inside remain fixed - how is this possible? I was under the impression that this smooth, frictionless connection between a rotating body and a stationary body was only really achievable through ball/roller bearings.
Just prior to this point in the video you can see that the display has been inserted from the front and this portion will be added from the back and screwed in. All that is required is to ensure that there is enough space between the two parts for the bezel flange not to be nipped. Many plastics have a low coefficient of friction with steel or nickel plating. Try sliding a stainless steel kitchen knife across various hard plastics and see what you find. (I've never touched a Nest so I don't know what I'm comparing with.)
Links:
