Introduction
Internal clearance and shaft/housing fits determine how a rolling bearing performs after installation. Incorrect clearance or fit can cause overheating, noise, premature wear or early failure.
This guide explains clearance groups and fit selection at methodology level. It complements the Industrial Bearing Selection Guide. Tolerance values, fit codes and clearance ranges are manufacturer-specific — confirm on the relevant catalogue before ordering.
Internal clearance groups
Internal clearance is the total distance one bearing ring can move relative to the other before mounting. After mounting, operational clearance (or preload) depends on shaft and housing fits and operating temperature.
| Group | Typical context |
|---|---|
| C2 | Less than normal clearance — tight applications where reduced play is required after mounting |
| CN (normal) | Default group for many general industrial applications at standard conditions |
| C3 | Greater than normal — common for tight interference fits or elevated operating temperature |
| C4 / C5 | Extra clearance — high temperature or special applications per manufacturer guidance |
Suffix letters on the bearing designation often indicate clearance group (for example C3). See bearing designation identification for suffix context.
Clearance group alone does not define installed behaviour. Interference fits on the shaft or housing reduce internal clearance; temperature differences between inner and outer ring also change operational clearance.
Shaft and housing fits
Fits control whether the ring rotates relative to its seat. The correct fit depends on load direction, rotation of inner vs outer ring, and whether the ring carries the circulating load.
| Fit concept | Typical use |
|---|---|
| Interference (tight) fit | Ring that carries rotating load should be tight on its seat to prevent creep |
| Loose (sliding) fit | Non-rotating ring or axial float location may use looser fit |
| Transition fit | Intermediate cases per manufacturer recommendation |
ISO tolerance zones (for example k5, m6, H7) are selected from manufacturer fit tables based on bore diameter, bearing type and load conditions. Do not copy fit codes from one application to another without engineering review.
Shaft considerations
- Surface finish and roundness affect fit performance.
- Step shoulders and retaining methods must secure the bearing axially where required.
- Hollow shafts may need different fit selection than solid shafts.
Housing considerations
- Split housings and pillow blocks have their own fit guidance in mounted unit catalogues.
- Housing material (steel, cast iron, aluminium) affects thermal expansion and fit behaviour.
Temperature and mounting effects
| Factor | Effect on clearance |
|---|---|
| Interference fit on inner ring | Reduces internal clearance |
| Interference fit on outer ring | Reduces internal clearance |
| Inner ring hotter than outer | Tends to reduce operational clearance |
| Outer ring hotter than inner | Tends to increase operational clearance |
| Mounting method | Induction heating, hydraulic mounting and press fits must follow manufacturer limits |
High-speed or high-temperature duty often requires C3 or greater clearance group to maintain positive operational clearance after mounting and thermal growth. Low-temperature or precision applications may need tighter control.
Specification workflow
- Confirm bearing type and size — from selection or identification workflow.
- Identify rotating ring — which ring carries the circulating load.
- Select shaft fit — per manufacturer fit table for load and rotation condition.
- Select housing fit — per manufacturer fit table.
- Choose clearance group — account for fits and operating temperature.
- Verify axial location — shoulders, locknuts, end covers or housing features.
- Document requirements on RFQ — bore, clearance suffix, fit specification and application data.
- Request engineering confirmation — via engineering enquiry.
Next steps
- For selection context, read the Industrial Bearing Selection Guide.
- For load and life basis, read Bearing Load Ratings Explained.
- For designation suffixes including clearance codes, read How to Read Bearing Designations.
- Review the relevant type authority for mounting notes.
Scope and limitations
- This article provides general clearance and fit methodology only.
- Numerical tolerance values and fit tables must come from manufacturer catalogue data.
- Mounted unit fits may differ from separate bearing fits — follow housing manufacturer guidance.
- Golden Bearing Company does not publish universal fit recommendations without application review.