1. Which ring sees a rotating load?
A ring subjected to a load rotating relative to that ring normally needs an interference fit to prevent creep.
Bridge Engineering technical guide
Shaft and Housing Fits for Bearings
A practical starting point for choosing common shaft and housing tolerances. Use the load direction, which ring rotates and whether axial movement is required before selecting a fit.
Engineering check required: the examples below are indicative, not a substitute for the bearing manufacturer’s tables. Final fits depend on bearing type and size, load, speed, temperature, internal clearance, housing material and installation method.
The three decisions that control the fit
2. Must either ring move axially?
In a locating/non-locating arrangement, the non-locating ring must be able to move in its seat unless axial movement is provided inside the bearing.
3. How severe is the duty?
Heavy, shock, reversing or vibrating loads usually require a firmer fit and a fresh internal-clearance check.
Common starting points
| Operating condition | Shaft starting point | Housing starting point | Why |
|---|---|---|---|
| Inner ring rotates; normal radial load | j5, k5 or k6 depending on size and duty | H7 for a stationary outer-ring load | Interference helps prevent inner-ring creep while the housing seat remains practical to assemble. |
| Inner ring rotates; heavy or shock load | Consider k6, m6 or a manufacturer-recommended firmer fit | H7 or firmer where the outer ring also sees demanding load | Higher load increases creep risk, but excessive interference reduces internal clearance. |
| Outer ring carries a rotating load | Fit selected for the inner-ring load condition | Interference fit such as K7/M7 may be required | The ring with rotating load normally needs the tighter seat. |
| Non-locating outer ring must slide axially | Interference where the inner ring has rotating load | Clearance-type housing fit, commonly H7 where suitable | Allows thermal expansion without loading both bearings axially. |
| Thin-walled, split or light-alloy housing | Check the shaft fit normally | Do not copy a solid-steel-housing fit blindly | Housing stiffness, thermal expansion and clamping distortion materially change the result. |
Tolerance symbols alone are not enough: the nominal diameter determines the actual upper and lower limits.
Before specifying a tolerance
- Confirm the exact bearing reference, size and internal-clearance suffix.
- Identify whether the load rotates relative to the inner ring, outer ring or both.
- Record normal and peak radial and axial loads.
- Check speed, temperature and the temperature difference between shaft and housing.
- Confirm whether the bearing is locating or non-locating.
- Check shaft and housing material, wall thickness and surface finish.
- Allow for the mounting method and available removal equipment.
- Use the current manufacturer catalogue for the final fit and tolerance limits.
Common fitting mistakes
Applying force through the rolling elements
Mounting force should pass through the ring being fitted. Transmitting force through balls or rollers can damage raceways before the machine starts.
Ignoring lost internal clearance
Interference and temperature differences reduce operating clearance. A tighter fit can require a different initial clearance class.
Restraining thermal expansion
Two axially locked bearings can create unintended preload as the shaft warms. Confirm the locating arrangement.