Bearing Shaft Tolerance
How common ISO 286 shaft and housing tolerance classes (h6, j6, k5, H7, J7) are chosen for bearing fits, and the shaft tolerance UC set-screw inserts need.
Shaft and housing tolerance classes under ISO 286 control how tightly a bearing’s bore and outside diameter fit onto the shaft and into the housing. The class chosen depends on which ring carries the rotating load, not on the bearing size alone.
Common classes and when they are used
| Fit | Common class | Typical case |
|---|---|---|
| Shaft, rotating inner ring load | k5 or k6 | Light to moderate interference; general industrial shafts, motor shafts |
| Shaft, lighter or easily removable fit | j6 | Where the inner ring does not need a full interference fit |
| Shaft, plain clearance (set-screw locked) | h6 to h9 | UC, SB and SA insert bearings, locked by set screws or collar, not by an interference fit |
| Housing, stationary outer ring | H7 | General industrial housings — easiest to fit and remove |
| Housing, lighter interference | J7 | Where some resistance to outer ring creep is wanted without a full press fit |
Exact micron values for each class change with the shaft or housing diameter under ISO 286; this table is for choosing which class applies to a given situation, not a substitute for checking the standard or a drawing’s stated tolerance.
Set-screw mounted units (UC, SB, SA)
Insert bearings that lock with set screws or an eccentric collar do not rely on an interference fit to hold position on the shaft, so the shaft itself only needs a plain commercial tolerance, not a press fit — see insert bearing for how the UC, SB and SA locking methods differ. This is different from a plain deep groove ball bearing pressed directly onto a shaft, where the shaft tolerance class matters more because it is the only thing holding the inner ring in place.
Send the shaft or housing diameter and how the load rotates to sales@fuli-bearings.com if you need help confirming which fit class applies to your application.
FAQ
Why does a rotating shaft need a tighter fit than a stationary housing?
A load that rotates with the inner ring tends to creep the ring around the shaft if the fit is loose, wearing both parts; a tighter fit (j6 or k5) stops this. The outer ring in a stationary housing does not rotate with the load, so a looser fit (H7 or J7) is normal and makes the bearing easier to fit and remove.
What tolerance class should I use for a UC insert bearing on a set-screw shaft?
UC, SB and SA inserts are bored for the shaft to pass through with a plain clearance fit, since the set screws (or eccentric collar on SA) do the locking, not an interference fit. A standard commercial shaft tolerance (such as h6 to h9 depending on how the shaft is otherwise used) is normally adequate — there is no need to machine a press fit for these inserts.
Where do I find the exact micron tolerance for a given shaft or housing diameter?
ISO 286 sets a micron range for each tolerance class at each diameter band, and the range changes with diameter. Check the standard directly or confirm with your drawing office for the exact figures; this page covers which class is normally chosen and why, not a full micron table.