The simplest hinge is a tube sleeved on the shaft and can swing around the shaft. But if we need this kind of tube in some occasions and it can "rotate" around our center, how should we design it? -So the ball head is like this.
The structure of the ball head is actually very simple. One end is a steel ball and the other end is a "ball bowl" (which can be understood as a "hollow ball").
The ball bowl just wraps the steel ball, and the steel ball can rotate freely in the ball bowl. In cars, the use of ball heads is very common. For example, the pull rod of steering gear and the joint of hanging swing arm are all concrete application examples of ball head.