Guide to Decoding and Selecting SKF Bearing Codes

If bearings are the heart of machinery, then bearing codes serve as the essential key to understanding this mechanical heart. With countless bearing models available, the ability to quickly and accurately identify their type, dimensions, precision, and other critical specifications becomes paramount for proper selection. This article examines SKF bearing codes in detail, providing insights into their structure to help professionals master bearing selection.

Bearing codes represent standardized identification systems used by manufacturers to classify their products. These alphanumeric sequences contain vital information about bearing type, dimensions, tolerance class, internal design, and special features. Correct interpretation enables engineers and maintenance personnel to quickly identify specifications, select appropriate replacements, and perform effective maintenance to ensure reliable equipment operation.

While numbering systems may vary between manufacturers, the fundamental principles remain similar. This analysis focuses specifically on SKF's comprehensive coding system.

The SKF bearing designation consists of two primary components: the basic designation and supplementary suffixes. The basic designation identifies the fundamental bearing type, dimension series, and bore diameter. Supplementary suffixes denote special features, tolerance classes, internal clearance, and other characteristics. These components are typically separated by a forward slash.

The basic designation typically comprises three to five digits or letters with the following structure:

• Bearing Type Code: Letters or numbers indicating the bearing category:
  • 6: Deep groove ball bearing
  • 7: Angular contact ball bearing
  • 2 or 3: Spherical roller bearing
  • N: Cylindrical roller bearing
  • NU: Cylindrical roller bearing (outer ring without flanges)
  • NJ: Cylindrical roller bearing (inner ring with single flange)
  • NN: Double row cylindrical roller bearing
  • QJ: Four-point contact ball bearing
  • T: Tapered roller bearing
• Dimension Series Code: Numeric values representing the bearing's size series, including outer diameter and width dimensions. Higher numbers indicate larger bearings (e.g., 0, 1, 2, 3).
• Bore Diameter Code: Numbers specifying the inner diameter. For diameters ≥20mm, this typically equals the bore size divided by 5 (e.g., 100mm bore = code 20). Special rules apply for diameters below 20mm.

Supplementary suffixes describe special features, precision classes, clearances, and other technical specifications. These alphanumeric codes appear after the basic designation, separated by a slash. Common suffixes include:

• Tolerance Class: Letters denoting precision grades (P0 = normal, P6, P5, P4, P2 with increasing precision)
• Internal Clearance: Letter-number combinations (C1, C2, C3, C4, C5) indicating radial play
• Internal Design: Letters/numbers specifying structural modifications (A = enhanced design, B = increased contact angle)
• Cage Type: Letters identifying cage materials/construction (J = pressed steel, M = machined brass, TN = polymer)
• Sealing: Letters describing sealing arrangements (2RS1 = dual rubber contact seals, ZZ = metal shields)
• Lubrication: Codes for pre-filled grease types
• Special Designs: Unique identifiers for application-specific variants (e.g., VA405 for rail vehicles)

Consider SKF bearing 6205-2RS1/C3:

• 6: Deep groove ball bearing
• 2: Dimension series
• 05: 25mm bore (5×5)
• 2RS1: Dual rubber contact seals
• C3: Greater than normal radial clearance

When selecting SKF bearings, professionals should evaluate multiple factors:

• Load Characteristics: Magnitude and direction (radial, axial, or combined) determine suitable bearing types and sizes
• Rotational Speed: Operational RPM affects service life and temperature rise
• Temperature Range: Environmental conditions influence lubrication requirements and material selection
• Lubrication Method: Oil or grease lubrication impacts maintenance schedules and longevity
• Space Constraints: Physical dimensions may limit bearing options
• Precision Needs: Application requirements dictate necessary tolerance classes

Understanding SKF's bearing numbering system forms the foundation for effective bearing selection and maintenance. By mastering code interpretation, professionals can efficiently identify specifications, source appropriate replacements, and implement proper upkeep procedures—all critical for maintaining optimal machinery performance. This knowledge empowers engineers and technicians to make informed decisions that enhance equipment reliability and operational efficiency.