Good "Small Cooling Fan" in addition to ventilation volume, high pressure outside, reliability is very important bearing in the form of a fan used in this very important quality. Always use high speed ball bearing fan and low-speed fan using low-cost oil bearing. Oil-bearing fan with only one bearing; and ball bearings "Small Cooling Fan" requires two bearings, single ball bearing, is "1 Ball + 1 Sleeve", oil-bearing components still have. More advanced than the single ball is a double ball bearing, namely Two Balls. With the long run, the oil inside the bearing will evaporate and dry, the friction coefficient increases, "Small Cooling Fan" operation affected may appear different sound, speed Pianman not even turn on. The ball bearing is replaced by rolling friction sliding friction, low coefficient of friction and to overcome the shortcomings of the friction coefficient is apt, therefore running stability, life is relatively much longer.