Industrial Bearing Identification & Designation Guide
A practical engineering manual for deciphering bearing part numbers across SKF, FAG, NSK, and Timken. Learn how to extract exact bore dimensions, internal radial clearance ratings, sealing configurations, and cage materials from stamped bearing rings.
Direct Answer: How to Read a Standard Bearing Number
Standard rolling bearing part numbers consist of three segments: the Bearing Type & Width Series (e.g. 6 = Deep Groove Ball; 22 = Spherical Roller), the Diameter Series (e.g. 2 = Light; 3 = Medium), and the Bore Code (last 2 digits multiplied by 5 for bore in mm, starting from 04). Suffixes specify essential mechanical modifications: 2RS indicates dual rubber contact seals, ZZ/2Z indicates dual non-contact metal shields, and C3 denotes enlarged internal radial clearance mandatory for electric motors.
Anatomy of an Industrial Bearing Designation
Example: Deciphering 6308-2RS1/C3
Bearing Type
Deep groove single row radial ball bearing (most versatile, handles radial and moderate thrust loads).
Dimension Series
Medium duty series (heavier cross-section and larger ball elements than 2 Series Light).
Bore Diameter
08 x 5 = 40mm inside diameter fitting a 40mm machined motor shaft.
Seals & Clearance
Dual synthetic rubber contact seals (2RS1) with C3 radial internal clearance (15–30 µm).
First Digit: Bearing Type Reference
Standard ISO 15 classification codes across global manufacturers.
| Code | Bearing Family | Primary Load Direction | Common Kenyan Plant Application |
|---|---|---|---|
| 6 | Deep Groove Ball Bearings | Radial + Light Axial | Electric motors, pumps, fans, gearboxes |
| 7 | Angular Contact Ball Bearings | High Combined Radial & Thrust | Multistage pump thrust brackets, machine spindles |
| 22 / 23 | Spherical Roller Bearings | Heavy Radial + Self-Aligning | Crushers, vibrating screens, conveyor head drums |
| 30 / 32 | Taper Roller Bearings | Heavy Radial & Heavy Thrust | Industrial reduction gearboxes, vehicle wheel hubs |
| N / NU / NJ | Cylindrical Roller Bearings | Pure Heavy Radial Only | Heavy electric motor drive-ends (> 55 kW) |
| 5 | Thrust Ball Bearings | Pure Axial Thrust Only | Crane hooks, turntable swivels, vertical screw jacks |
Essential Bearing Suffix Decoder
Never order a bearing by base number alone; suffixes dictate operational suitability.
Internal Radial Clearance Suffixes
- C1 / C2:Less clearance than Normal (used in high-precision machine tool spindles).
- CN (Normal):Standard clearance (often omitted in part number). Suitable for slow-speed ambient drives.
- C3:Enlarged clearance. Mandatory for electric motors, vibrating machinery, and hot shafts.
- C4 / C5:Extra-large radial clearance for kiln rollers, furnace fans, and drying stenters exceeding 120°C.
Sealing & Shielding Suffixes
- Z / 2Z / ZZ:Non-contact pressed steel shields on one or both sides. High speed, low friction, grease retained.
- RS1 / 2RS1 / 2RS:Rubber contact seals (NBR) with steel reinforcement. Maximum exclusion of water and dust.
- RSH / 2RSH:Heavy-duty dual lip contact seals for harsh agricultural and quarry conditions.
- Open (No suffix):No shields or seals. Must be lubricated externally via oil bath or housing grease cavity.
Cage / Retainer Material Suffixes
- J (Standard):Pressed stamped steel cage. Standard on catalog ball bearings.
- M / MA:Machined brass cage. Essential for high vibration, reciprocating pumps, and centrifuges.
- TN9 / TVH:Glass-fiber reinforced Polyamide 66 cage. Quiet running, low mass, temperature limited to 120°C.
Special Performance & Housing Features
- W33:Lubrication groove and three grease holes in outer ring of spherical roller bearings.
- K:Tapered bore (1:12 taper) mounted onto adapter sleeves (H-series).
- INSOCOAT / VL0241:Electrical insulation coating on outer ring preventing VFD harmonic fluting damage.
Related Engineering Articles & Sourcing Guides
Preventing Counterfeit Bearings: SKF Authenticate App & Inspection Protocols
Step-by-step verification methodology used by plant engineers across Kenyan manufacturing facilities to confirm authentic metallurgy and packaging.
NSK & Timken Bearings in Kenya: Genuine Sourcing & Getting the Right Fit
Detailed breakdown of taper roller bearing numbers, millimeter and inch cup/cone matching, and suffix decoders for heavy process machinery.
Frequently Asked Questions: Bearing Identification
For standard metric bearings with bore codes 04 and above, multiply the last two digits by 5. For example: 6205 has a bore of 05 x 5 = 25mm; 6312 has a bore of 12 x 5 = 60mm. Special exceptions apply to the first four sizes: 00 = 10mm, 01 = 12mm, 02 = 15mm, and 03 = 17mm.
C3 clearance provides greater internal radial play than Normal (CN) clearance (typically 15–30 microns vs 8–18 microns on a 6208 bearing). When an electric motor reaches continuous operating temperatures, the shaft and inner ring expand faster than the housing. Normal clearance bearings pinch the rolling elements when hot, causing rapid overheating and seizure.
Choose 2RS (contact rubber seals) for wet, washdown, dusty, or slurry environments where water and grit exclusion is paramount (limited to ~70% of maximum catalog speed). Choose ZZ (non-contact steel shields) for dry, clean, high-speed, and high-temperature applications where seal friction and heat generation must be minimized.
The W33 suffix indicates an annular lubrication groove and three lubrication holes machined into the outer ring. This enables grease or oil replenishment directly between the two rows of spherical rollers via a grease nipple on the bearing housing.
Need Fast Identification or Sourcing for Industrial Bearings?
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