What is ball bearing?

In the bearing there are several little steel balls around, so when axle rotates, the steel balls rotate too. As it's round, its friction is also less than sleeve bearing design. You can also rule out the disadvantage of leaking oil, so the life in use is longer. Generally 40000~55000 hours. However, its cost is higher and that's why a cooler with ball bearing fan is about US$1~1.5 dollars more than sleeve bearing cooler.