Keep the evidence with the model shortlist
The models on this page illustrate bearing roles; they are not confirmed replacements for an unspecified machine. Keep the original complete marking, machine position, load and speed duty, temperature, lubricant and mounting arrangement together. Check the candidate's recorded values below and leave unreported parameters unknown.
Check drawings and model records · Investigate a failure before replacing it · Plan installation and force paths
What matters in this application
Load at each end
Separate rotor weight, belt pull and coupling forces. A direct-coupled motor and a belt-driven motor do not have the same bearing reactions.
Hot running condition
Record shaft and housing temperatures, fits and initial clearance. C3 is not a universal upgrade for every motor.
Electrical environment
For inverter-fed equipment, investigate shaft voltage and the complete grounding/insulation arrangement; ordinary steel bearings do not provide electrical isolation.
Which bearing structures make sense?
Deep groove ball bearings
A starting point for moderate radial loading and limited axial location.
Check first: Check the permissible axial load, noise requirement and grease/seal specification.
NU cylindrical roller bearings
A radial-support candidate when belt load or radial capacity drives the design.
Check first: An NU bearing is not the axial locating bearing; minimum load and axial freedom must be checked.
Insulated or hybrid designs
Investigate when electrical discharge damage has been identified.
Check first: Choose the specified insulated component within the whole motor system, not by bore alone.
Recommended starting points
These candidates illustrate specific roles and envelopes, not a ranked list or interchangeable set. Review each condition before using a model in a design.
6205
25×52×15 mm25 mm shaft · compact radial support
A compact deep-groove reference for a 25 mm seat when the calculated reactions and life permit this envelope.
- Dynamic C
- 14.8 kN
- Static C₀
- 7.8 kN
- Limiting speed
- 18000 rpm
Before selectionThis record is the unsuffixed bearing. Match the required seals, grease, clearance and temperature class.
Open complete model data6206
30×62×16 mm30 mm shaft · lighter 62-series envelope
Useful as a 30 mm-bore baseline before deciding whether a larger outside diameter is needed.
- Dynamic C
- 20.3 kN
- Static C₀
- 11.2 kN
- Limiting speed
- 15000 rpm
Before selectionDo not interchange it with 6306: housing diameter and width differ.
Open complete model data6306
30×72×19 mm30 mm shaft · larger radial envelope
A larger-envelope candidate to compare against 6206 where housing space and the load calculation justify it.
- Dynamic C
- 30.5 kN
- Static C₀
- 16.2 kN
- Limiting speed
- 13700 rpm
Before selectionConfirm the 72 mm housing seat, 19 mm width and the full motor-specific suffix.
Open complete model dataNU 206 ECJ
30×62×16 mm30 mm shaft · non-locating radial support
A cylindrical-roller option to investigate for radial support with axial displacement inside the bearing.
- Dynamic C
- 44 kN
- Static C₀
- 36.5 kN
- Limiting speed
- 14000 rpm
Before selectionProvide axial location elsewhere and verify minimum load, clearance and lubrication.
Open complete model dataCompare the recorded specifications
Different sizes and bearing structures are shown for different duties. C and C₀ are catalogue load ratings, not permissible equipment loads. Limiting speed is not an approved operating speed.
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| Parameter | SKF6205 | SKF6206 | FAG6306 | SKFNU 206 ECJ |
|---|---|---|---|---|
| Bore d (mm) | 25 | 30 | 30 | 30 |
| Outside D (mm) | 52 | 62 | 72 | 62 |
| Recorded width (mm) | 15 | 16 | 19 | 16 |
| Dynamic C (kN) | 14.8 | 20.3 | 30.5 | 44 |
| Static C₀ (kN) | 7.8 | 11.2 | 16.2 | 36.5 |
| Catalogue limiting speed (rpm) | 18000 | 15000 | 13700 | 14000 |
— = not reported, or not directly comparable for a mounted unit. Width conventions differ for inserts, complete units and bearing assemblies; inspect the dimensional drawing. Values are read from the current BearingScope records, not estimated from model numbers.
Work through the selection
- Record the complete old designation and identify the locating and non-locating ends from the motor drawing.
- Calculate bearing reactions from rotor weight, belt tension and overhung distances rather than using motor power as bearing load.
- Check life, minimum load and operating clearance, then assess grease, seals and electrical protection.
- Validate fits and installation forces; establish a temperature and vibration baseline after controlled commissioning.
Symptoms worth checking
Regular fluting or washboard marks
Investigate electrical discharge and shaft-current paths before replacing the same standard bearing.
Temperature rise after a bearing change
Review grease quantity, fits, residual clearance, preload and seal friction.
Drive-end vibration under belt tension
Check pulley alignment, tension and shaft reactions before simply increasing bearing size.
Symptoms are investigation prompts, not a diagnosis. Isolate equipment safely and follow its maintenance procedures before inspection.
Have the original designation?
Look up the complete model and suffix before comparing potential alternatives.
Application questions, answered
Can I find a bearing size from motor horsepower alone?
No. Motors with the same HP or kW rating can use different frames, shafts, drives and bearing arrangements. Obtain the motor model, frame, drive-end/non-drive-end position and original bearing designation before searching the catalogue.
Is C3 required in every electric motor?
No. Required initial clearance depends on interference fits, temperature differences and the intended operating clearance. Retain the specified grade unless the design calculation supports a change.
Can 6206 replace 6306?
They share a 30 mm bore in these records, but their outside diameters and widths differ. They are different installation envelopes, not direct replacements.
Does the listed limiting speed equal an approved motor speed?
No. Catalogue limiting speed is not an application approval. Lubrication, load, seals, thermal balance and the assembled motor impose additional limits.
Reference basis & recommendation limits
- SKF — Rolling bearings and seals in electric motors and generators
- NSK — Industrial Motors
Application principles are informed by the listed technical references. Model shortlists are BearingScope editorial selections from its database, not manufacturer endorsements or equipment-fit approvals. Confirm the latest exact specification and the complete equipment design before use.