Bearing fits chart
Recommended shaft and housing tolerances for mounting rolling-element bearings. The correct fit keeps the bearing rings firmly seated without over-tightening, which would pinch the internal clearance and shorten bearing life.
Shaft fits (rotating inner ring)
| Load | Shaft tolerance | Notes |
|---|---|---|
| Light (P up to 0.06 C) | j6 / js6 | Small bearings, light or variable loads |
| Normal (0.06 to 0.12 C) | k6 | The usual choice for general machinery |
| Heavy (over 0.12 C) | m6 / n6 | Heavy or shock loads, larger bearings |
Housing fits (outer ring)
| Condition | Housing tolerance | Notes |
|---|---|---|
| Stationary outer, normal load | H7 | Outer ring can slide for thermal movement |
| Outer must move axially | G7 / H7 | Floating bearing of a pair, free to shift |
| Rotating load on outer | M7 / N7 | Outer ring gripped, located bearing |
Choose which ring rotates relative to the load: the ring that sees a rotating load gets the tighter interference fit so it cannot creep. C is the bearing dynamic load rating and P is the equivalent applied load. These are general guidelines; follow the bearing maker tables for a specific application.
Pressing a plain shaft or hub instead?
For solid interference assemblies rather than bearings, see the Press Fit Chart for ISO and inch fit classes.
Why bearing fits matter
A rolling bearing has a designed internal clearance. If a ring is pressed onto an oversized shaft or into an undersized housing, that clearance shrinks, the balls or rollers preload, and the bearing runs hot and fails early. Too loose, and the ring creeps and wears its seat. The recommended fits hit the middle ground.
Rotating ring gets the tight fit
The ring that turns relative to the load direction must not slip on its seat, so it gets an interference fit. The stationary ring can take a looser fit, which also lets one bearing of a pair float to absorb shaft expansion. Identifying which ring rotates under load is the key to picking the fit.
FAQ
What shaft fit is normal for a bearing?
A k6 shaft tolerance suits most general machinery with a rotating inner ring under normal load. Lighter loads use j6, heavier loads use m6 or n6.
Why can a too-tight bearing fit cause failure?
Excess interference squeezes the bearing internal clearance and preloads the rolling elements. That raises friction and heat, and the bearing can overheat and fail well before its rated life.
Should both bearings on a shaft be tight?
Usually no. One bearing is located with both rings fixed, and the other floats with a looser housing fit so it can slide as the shaft grows with temperature. Fixing both can bind the shaft.