Double ball bearings are relatively high-grade bearings. There are several tiny steel balls around the shaft in the bearing. When the fan or the shaft rotates, the steel ball rotates. Because they are all spheres, the friction is small and there is no problem with oil leakage. The advantages of the double ball fan are long life, about 40,000 to 55,000 hours; good anti-aging performance, suitable for fans with higher speed. The disadvantage of double ball bearings is the high manufacturing cost and the highest noise at the same speed level (because the ball bearing friction points are increased by a factor of 2.)
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