1, depending on the use conditions, whether the outer ring is fixed or the inner ring is fixed. For example, the wheel and the inner ring are fixed on the shaft, and the shaft is fitted with h7, so that it can move slightly on the shaft, and it will not be fixed if it is worn.

2, transmission device or machine tool spindle, requires slight movement of the shell, shaft with transition fit or tight fit, generally with interference fit as the precision requirement.

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Fit tolerance (fit? Tolerance) refers to the sum of the tolerances of the holes and shafts that make up the fit. This is the allowable deviation of clearance or interference. The size and position of the hole and shaft tolerance zone constitute the fitting tolerance. The fit tolerance of hole and shaft indicates the fit accuracy of hole and shaft. The size and position of the tolerance zone between the hole and the shaft indicate the matching accuracy and matching characteristics of the hole and the shaft. The size of the fit tolerance = the size of the tolerance zone; Size and position of the tolerance zone = fit characteristics.

References:

Tolerance standardization and technical measurement of interchangeability conditions