Ever struggled to decode tapered roller bearing size charts? You’re not alone. Many engineers and buyers waste hours interpreting numbers that could take minutes.

Tapered roller bearing dimensions follow standardized codes indicating bore diameter, width, and outer diameter. The key is understanding how bearing numbers map to actual measurements in millimeters or inches.

Let me break down the system so you can instantly identify any tapered bearing’s size – whether you’re reviewing technical drawings or replacing worn components.

How do you read roller bearing numbers?

That cryptic alphanumeric code on your bearing isn’t random. Each character reveals critical sizing information if you know the pattern.

Standard tapered roller bearings¹ use a numbering system where the last two digits multiplied by 5 give the bore diameter² in mm. Prefixes/suffixes indicate series, design variants, and clearance classes.

Understanding the Basic Numbering Structure

Most manufacturers follow these conventions:

Code Segment	What It Shows	Example (30206 Bearing)
First Digit	Bearing type & series	"3" indicates tapered roller
Next Two Digits	Dimension series	"02" means light series
Last Two Digits	Bore size code	"06" = 30mm bore (6×5)

The complete breakdown:

1. Type Identifier (First Digit)

   • 3: Tapered roller bearing
   • 7: Angular contact bearing
   • 6: Deep groove ball bearing

2. Dimension Series (Next Two Digits)

   • Width/Diameter combinations:
     • 00: Extra light
     • 02: Light
     • 03: Medium
     • 04: Heavy

3. Bore Size (Last Two Digits)

   • Multiply by 5 for mm bore:
     • 00 = 10mm
     • 01 = 12mm
     • 02 = 15mm
     • From 03 onward: Code × 5 = mm

Special cases:

• Bore sizes under 10mm use actual mm (e.g., 608 = 8mm bore)
• Inch series bearings have different prefixes (LM, HM, etc.)

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How do you measure a tapered roller bearing?

Guessing dimensions leads to costly mistakes. Here’s the professional measurement method we use in our factory.

Measure tapered roller bearings¹ using calipers on clean, undamaged surfaces. Record inner diameter (ID), outer diameter (OD), and width – noting which are tapered surfaces versus straight edges.

Step-by-Step Measurement Protocol

1. Preparation

   • Clean bearing surfaces (remove grease/debris)
   • Use calibrated digital or vernier calipers²
   • Support bearing evenly during measurement

2. Critical Dimensions to Capture

Dimension	Measurement Technique	Tolerance Standards
Bore Diameter (ID)	Measure at 3+ points along straight section	ISO 492 Class 4
Outer Diameter (OD)	Record maximum diameter of outer ring	ABEC 3/ISO P6
Width	Measure both rings separately under load	DIN 620-2

3. Special Considerations for Tapered Bearings

   • Cup/Cone Distinction:
     • Cups (outer rings) have tapered inner surfaces
     • Cones (inner assemblies) have tapered outer surfaces
   • Contact Angle Measurement:
     • Critical for load capacity calculations
     • Use angle protractor between cup and cone

4. Common Measurement Errors

   • Mistaking tapered surfaces for diameter points
   • Not accounting for chamfers/radius edges
   • Measuring worn bearings without wear compensation

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How do you determine bearing size with dimensions?

Matching physical measurements to standard sizes prevents compatibility issues in machinery repairs.

Cross-reference your measured ID, OD, and width against ISO dimension tables¹. Most tapered roller bearings follow ISO 355 standards for metric series or ANSI/ABMA 19.1² for inch series.

Navigating Standard Size Tables

1. Metric Series (ISO 355)

Key columns in dimension tables:

Bearing Number	d (mm)	D (mm)	T (mm)	B (mm)	C (mm)
30205	25	52	16.25	15	13

Where:

• d = Bore diameter
• D = Outer diameter
• T = Assembly width
• B = Inner ring width
• C = Outer ring width

2. Inch Series (ANSI/ABMA 19.1²)

Common series include:

• LM (Light Medium)
• HM (Heavy Medium)
• L (Light)

Example conversion:

Bearing Designation	Bore (inches)	OD (inches)	Width (inches)
LM67048	0.75	1.5625	0.4375

3. Non-Standard Sizing
   • Custom bearings may deviate from standards
   • Always verify with manufacturer drawings
   • Check for suffix modifications:
     • /A: Altered internal clearance
     • /W33: Lubrication groove

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Conclusion

Mastering tapered roller bearing dimensions ensures correct replacements and prevents machinery failures. Remember: decode numbers systematically, measure precisely, and cross-reference with standards.