There is a bearing on each side of the hub.
Cup and cone ball bearings.
Round ball bearings roll on the curved surface of the cup and cone.
Steel balls roll between these two parts.
The surfaces are cut typically by grinding.
Even the highest quality bearing surfaces will have slight grinding marks.
The combination of cup cone and balls forms the bearing.
Top quality ball cup cone bearings are offered in this comprehensive source of manufacturers distributors and service companies for the industrial marketplace.
In the left image below is a high quality cone magnified two hundred times.
The cups are built into the shell of the hub.
Cup cone sets bearings lm11749 lm11710 cup cone tapered bearing set brand new dura roll tapered bearing cup and cone set.
Cup cone bearing.
If the cones are screwed on too far they exert pressure on the bearing balls.
Angular contact bearings also allow easier maintenance adjustability and serviceability.
Bearing surfaces are made from hardened steel.