I've been unable to find a clear explanation of the design principle behind a ball bearing door hinge.
In the image below, the casing for a ball bearing assembly is highlighted.
What is inside this casing? How are the ball bearings distributed/attached inside?
I'm also wondering about their durability, given that the mechanism isn't solid metal, but has internal (presumably moving) components under the casing. How thick is the casing, and does it carry all of the vertical load, or is the load shared with the internal components/ball bearings?