The size of inner clearance has great influence on the performance of bearing, such as fatigue life, vibration, temperature rise, noise and so on. The curve below shows the relationship between the working clearance and fatigue life of bearing. It can be seen that during operation bearing life can be the largest when working clearance is slightly less than zero. However, due to the influence of bearing precision and the temperature rise in operation, the clearance of bearing will be reduced accordingly, which will cause bearing heat and the decrease of bearing service life.