????Bearing internal clearance is defined as the total distance through which one ring can be moved radially(radial internal clearance) or axially(axial internal clearance) relative to the other ring under a certain measuring force. ????It is necessary to distinguish between the internal clearance of a bearing before it is mounted and the internal clearance of a mounted bearing in operation(working clearance). Because the rings are mounted with interference or transition fit, the rings will expand or compress, the bearing’s initial clearance is always larger than the working clearance. ????If the bearing is mounted with recommended fit and runs under the normal condition, the normal group of initial internal clearance is appropriate to the bearing’s working clearance . If the inner and outer rings are mounted with interference fit or the working temperature is higher or lower, we can select larger or smaller clearance value than the normal group.