What do numbers on bearings mean?

If you’ve ever looked at the side of a rolling-element bearing, you’ve likely seen a string of alphanumeric characters like 6204-2RS or 25BC02. To the untrained eye, these look like random codes. In reality, they are a precise language that describes the bearing’s dimensions, internal design, and sealing. Understanding these codes is crucial correct selection, replacement, and interchange. Whether you are maintaining industrial equipment, designing machinery, or sourcing replacements. However, the complexity increases when you realize that different global standards specifically ABMA and ISO (SKF) use different "languages" to describe the same part. ABMA (American Bearing Manufacturers Association): Historically used more frequently in North American inch-series and specific military/industrial applications. These codes can be long and complex, often looking like 25BC02.

While

ISO (International Standards Organization): The global standard used by manufacturers like SKF. These are usually shorter, metric-based codes like 6205. Anatomy of ABMA Bearing number. As stated earlier a typical ABMA bearing number would look like this 25BC02JPPY3 so let's break it down. 1. The Bore Size (25)

The first two digits represent the bore diameter in millimeters. In this case, the inner hole of the bearing is exactly 25mm. 2. The Type Code (BC)

This is the most critical part of the identification. It tells you the internal construction. While BC (Single Row Radial, Conrad-type) is the most common, there are many others:

• BA: Single Row, Angular Contact (handles both radial and axial loads).

• BS: Self-Aligning Ball Bearing (for applications with shaft misalignment).

• BL: Single Row Radial, Filling Slot (higher radial capacity, but lower speeds).
• BT: Angular Contact, High Angle (specifically for heavy thrust).

3. Dimension Series (03)

These digits indicate the "duty" or the physical robustness (Width and Outside Diameter).

• 02: Light Duty.

• 03: Medium Duty.

• 04: Heavy Duty.

4. Shields, Seals, and Suffixes (JPPY)

The letters at the end describe how the bearing is protected and what it contains. You might assume PP is the only protection available, but the system is much broader:

• J: Pressed Steel Cage (keeps the balls separated).

• P / PP: One or two Metal Shields.

• D / DD: One or two Contact Seals (rubber/synthetic).

• Y: Modification code (often referring to standard clearance or grease).
• 3: Corresponds to a standard clearance that allows for allows for heat expansion.

Anatomy of ISO Bearing number. 1. The First Digit: Bearing Type (6)

The very first number tells you the basic design

6: Single Row Deep Groove Ball Bearing (The most common).

7: Single Row Angular Contact Ball Bearing (Used for thrust).

N: Cylindrical Roller Bearing (Used for high radial loads, often found in heavy gearboxes).

2. The Second Digit: Dimension Series (2)

This digit indicates the "robustness" or cross-section of the bearing.

• 0 or 1: Extra Light.

• 2: Light.

• 3: Medium.

• 4: Heavy.

3. The Last Two Digits: Bore Code (05)

For most bearings, you multiply these two digits by 5 to get the bore diameter in millimeters.

Example: 05 x 5 = 25mm.

Important Exception: The "Miniature" Bore Rules For small shafts, the "multiply by 5" rule does not apply.

You must memorize these four specific codes:

• 00 = 10 mm

• 01 = 12 mm

• 02 = 15 mm

• 03 = 17 mm

4. The First Suffix: Sealing (ZZ)

Letters after the dash indicate how the bearing is protected.

• Z: One metal shield.

• ZZ (or 2Z): Two metal shields.

• RS1: One rubber contact seal.

• 2RS1: Two rubber contact seals.

5. The Final Suffix: Internal Clearance (/C3)

The code after the slash indicates the internal "play" or room for thermal expansion.

• Standard (No code): Normal clearance.
• C3: Greater than normal (essential for high-speed or high-heat motors).

Manual conversion is risky. A single digit error can lead to ordering a bearing with the wrong clearance or seal type, resulting in catastrophic equipment failure.

To bridge this gap, we developed the ABMA to SKF Conversion Tool. This tool is designed for engineers and procurement specialists who require high-precision interchanges. ABMA to SKF Tool Also take a look at this scribd document. https://www.scribd.com/document/482768204/Conversion-AFBMA-to-SKF#:~:text=Bearing%20Interchange%20From,Same%20side%20as%20Seal/Shield