Why is correct bearing fit important?

Correct bearing fit ensures the ring with rotating load has an interference fit to prevent creep (ring rotation on the seat), while the non-rotating ring has a looser fit for easy mounting and to allow axial float if needed.

What is a rotating inner ring load?

Rotating inner ring load is the most common case — the shaft rotates and the housing is stationary. The inner ring needs a tight (interference) fit on the shaft, and the outer ring gets a sliding or transition fit in the housing.

What tolerance zone should I use for a shaft?

For rotating inner ring load with normal conditions: j5 or k5 for light loads on ball bearings, k5 or m5 for normal loads, m6 or n6 for heavy loads or vibrations. The tighter the fit, the more force required for mounting.

What is the difference between transition and interference fit?

A transition fit (e.g., j5, k5) may result in either slight clearance or slight interference. An interference fit (e.g., m5, n6, p6) always results in the shaft being larger than the bore, requiring force or heating for assembly.

When should I use a loose housing fit?

A loose housing fit (e.g., H7, G7) is used when the outer ring must be free to move axially (non-locating bearing position), when the housing is split, or when the outer ring load is stationary (rotating shaft, fixed housing).

Free Engineering Tool #048

Bearing Fit & Tolerance Selection

Select recommended shaft and housing tolerance zones for bearing mounting per ISO 12129. Choose load type and bearing bore diameter.

ISO 12129 Shaft & Housing Fits Tolerance Zones

Bearing Bore Diameter (mm)

Load Condition

Bearing Type

Axial Position

Quick presets

Recommended Fits

Shaft Tolerance Zone

—

Housing Tolerance Zone

—

Fit Type — Shaft

—

Fit Type — Housing

—

Mounting Note

—

General Principle

The ring subjected to rotating load should have an interference fit to prevent creep. The ring with stationary load can have a looser fit for ease of mounting and axial displacement.

Shaft Fit Recommendations (Rotating Inner Ring)

Load	Ball Bearings	Roller Bearings	Fit Type
Light / variable direction	j5, j6	j5, j6	Transition
Normal	k5, k6	m5, m6	Transition / Light interference
Heavy / shock	m5, m6	n6, p6	Interference

Housing Fit Recommendations (Stationary Outer Ring)

Condition	Locating	Non-locating	Fit Type
Normal loads	J7, H7	H7, G7	Sliding / transition
Heavy loads	K7, M7	H7, J7	Transition
Light, easy dismount	H7	G7, F7	Clearance
Rotating outer ring	M7, N7	K7, M7	Interference

ℹ️ Tip: For bearings with bore d > 100 mm, the next tighter tolerance class is often recommended due to the lower relative interference. Hollow shafts also require tighter fits.

⚠️ Note: These are general recommendations. Always verify with the specific bearing manufacturer’s guidelines (SKF, FAG/Schaeffler, NSK, Timken) for your application.