The radial internal clearance applies to bearings with an inner ring before the bearing is fitted. It is defined as CN, C2, C3, C4, C5 Internal clearance groups.
Internal clearance is the play within a ball bearing. It is the geometrical low torque. High loads. Heavy interference fits. High temperature. Preloaded. C3,C4,C5
C3，C4. 8.2.1 Criteria for selecting bearing internal clearance. A bearing's life is theoretically maximum when operating clearance is slightly negative at steady.
C2, Less than Normal. CN, Normal, only used in combination with letters indicating reduced or displaced clearance range. C3, Greater than Normal. C4, Greater