A bearing housing bore needs a fit that holds the outer ring under its operating load while allowing the movement required by the bearing arrangement. The right tolerance is not selected from bearing outside diameter alone. Load direction, load magnitude, temperature, accuracy and whether the ring must slide axially all affect the choice. This table summarizes selected SKF recommendations from Tables 4 and 5 for metric radial ball and roller bearings in cast-iron or steel housings.

Metric bearing housing fit classes

Understand the conditions first

SKF expresses some load conditions relative to the bearing’s basic dynamic load rating C. In the table, P is the equivalent bearing load and P/C is dimensionless. The catalogue distinguishes a stationary outer-ring load from a rotating outer-ring load and from cases where the load direction is indeterminate. These descriptions refer to the load direction relative to the ring, not simply whether the shaft or housing is visibly rotating.

For a stationary outer-ring load, SKF lists H7 for loads of all kinds, and H8 for light to normal loads under simple working conditions. A J7 class is shown for an indeterminate load direction with light to normal load when outer-ring axial displacement is desirable. Heat conducted through the shaft is listed separately with G7. These are conditional recommendations, not an ordinal ranking where a higher or lower letter is always “tighter” for every size.

Rotating and indeterminate loads

When the outer-ring load rotates, the ring may need a tighter housing fit to prevent creep. SKF lists P7 for heavy loads in thin-wall housings or heavy shock conditions above 0.10 C, N7 for normal to heavy loads above 0.05 C, and M7 for light variable loads at or below 0.05 C. These example classes are tied to the stated conditions and examples in the catalogue; do not transfer them to a different housing material or load arrangement without checking the full recommendation.

For an indeterminate load direction, SKF lists M7 for heavy shock and K7 for normal or heavy loads above 0.06 C when axial displacement is unnecessary. In contrast, if accuracy or quiet running is the priority, the catalogue shows selected classes by bearing type and adjustment condition, including J6 for ball bearings, JS5 for tapered roller bearings adjusted through the outer ring, K5 for an axially located outer ring and M5 for rotating outer-ring load. The intended condition must accompany the symbol.

Fit class versus bore size limits

A class such as H7 is a tolerance designation, not a finished bore diameter. To determine upper and lower limits, combine the nominal bearing outside diameter with the correct tolerance table and diameter interval. SKF directs readers to Table 9 for specific housing-bore values. The product must also satisfy the bearing’s required form, surface finish, roundness and alignment. A fit symbol by itself does not specify all those characteristics.

Application checks

Before setting a drawing tolerance, confirm the bearing’s dimensional class and exact type, the load ratio, which ring sees a rotating load, whether the outer ring must float, housing material and whether the housing is split. Temperature differences can change the practical fit; SKF gives additional guidance for large bearings and temperature gradients. Thin-walled rings and smaller bearings may require tighter roundness or dimensional accuracy. Read the notes attached to the specific table row rather than treating the class as an isolated answer.

These recommendations apply to the catalogue’s stated metric radial bearing scope and nominal bearing classes. Thrust bearings, higher-precision bearings, non-ferrous housings, unusual thermal conditions and special arrangements have separate guidance. Use SKF’s current full catalogue or application engineering for the final fit, and verify the machined bore by measurement before assembly.