The reason to start with deep groove ball bearings is that several bearings 6204 have been bought in the last few days.Below the rolling bearing branch are radial bearings, radial bearings include deep groove ball bearings or radial ball bearings. The bearing bore dimensions of the base bore system are negative tolerances.
The following two paragraphs are also taken from the Mechanical Design Manual.
In order to prevent undue relative slippage between the inner ring and the shaft, the outer ring and the housing hole during machine operation, the correct fit must be selected. Usually a properly tight fit between the shaft and the inner ring is the easiest and most effective way to prevent the shaft from sliding relative to the inner ring. Especially for the thin-walled bearing ring, the use of appropriate tight fit can make the bearing ring in motion uniform force, so that the bearing load carrying capacity can be given full play. However, the bearing fit should not be too tight, because the elastic expansion of the inner ring and the contraction of the outer ring of the bearing radial clearance is reduced and completely eliminated, thus affecting normal operation.
For the fit of bearing bore d to the shaft, take the base hole system, but the tolerance zone is below the zero line, i.e. the upper deviation is zero, which makes it easier to obtain a tighter fit than the general base hole system. The tolerance zone of the outer diameter D and the hole of the housing is taken from the base shaft system, which is located below the zero line and has an upper deviation of 0, as in the general base shaft system, but the tolerance zone is not exactly the same as in the general tolerance system. The fit of the bearing to the bore is generally loose compared to the shaft.
The blackened is the complete sentence, it can be considered that the negative tolerance of the bearing bore system is in order to obtain a tighter fit under the same name, and this fit is not too tight to affect the normal operation of the bearing. So that in the clearance fit of the same name can be achieved to reduce the clearance amount or reach the transition fit, in the transition fit of the same name can be achieved to overload fit and do not affect the operation of the bearing because of the large amount of overload.
Our common rolling bearings are rarely used in the overfit of the same name as in Figure 1, and generally have a certain amount of overfit in the clearance or overfit of the same name.
Also the tolerance zone of the radial ball bearing is different from the normal bore system and is intended to be a tight fit and not too tight. Ordinary Class 0 bearings are not generally marked on the bearing.
The outer ring size of Class 0 bearing 6204 is 47 and its lower deviation is 0.009, which is smaller than that of H7, so the clearance of the fit is smaller.