Bearing identification: designations, suffixes and dimensions

Ordering a replacement bearing seems simple until the marking is worn or the suffix is unfamiliar. Most rolling bearings follow a designation system based on ISO standards, extended by each manufacturer with its own prefixes and suffixes. Understanding that system lets you order the right bearing the first time.

The structure of a bearing designation

A typical designation has 3 parts:

1. Prefix (optional): describes components or special variants, for example a separate inner or outer ring.
2. Basic designation: describes the bearing type, the dimension series and the bore size.
3. Suffix (optional): describes design details such as seals, cage, internal clearance, precision or heat treatment.

The basic designation is largely standardized; prefixes and suffixes are partly manufacturer specific, which is where most mistakes happen.

Reading the basic designation

Take the common bearing 6205 as an example:

• 6 is the bearing type: a single row deep groove ball bearing.
• 2 is the dimension series. It indicates the outside diameter and width relative to the bore.
• 05 is the bore code. For bore codes from 04 upward, the bore in millimeters is the code multiplied by 5, so 05 means a 25 mm bore.

The result is a deep groove ball bearing with a 25 mm bore, 52 mm outside diameter and 15 mm width. A 6305 has the same bore but belongs to a heavier series, with a 62 mm outside diameter and 17 mm width.

Bore codes below 04

Small bearings use fixed codes:

Very small bearings and some large ones use the bore diameter directly, sometimes separated by a slash (for example 618/500 has a 500 mm bore).

Common type codes

The first digit or letters usually identify the bearing type:

• 1: self-aligning ball bearing
• 2: spherical roller bearing (for example 22220) or self-aligning ball bearing, depending on the series
• 3: tapered roller bearing or double row angular contact ball bearing, depending on the series
• 5: thrust ball bearing
• 6: single row deep groove ball bearing
• 7: single row angular contact ball bearing
• N, NU, NJ, NUP: cylindrical roller bearings with different rib arrangements

Tapered roller bearings are often designated under a separate system (ISO 355) or by inch series part numbers, so a tapered bearing may carry a completely different style of marking.

Common suffixes

Suffixes are where 2 bearings with the same basic number can be completely different parts. Some frequent examples:

Seals and shields

• Z or 2Z, ZZ: metal shield on 1 or both sides.
• RS, 2RS and manufacturer variants such as 2RS1 or 2RSH: contact rubber seal on 1 or both sides.
• RZ or similar: low friction non contact seal (naming varies by manufacturer).

Internal clearance

• C2: clearance smaller than normal.
• No marking (CN): normal clearance.
• C3: clearance greater than normal, common in electric motors and applications with heat.
• C4, C5: progressively larger clearance.

Replacing a C3 bearing with a normal clearance one in a hot running motor can cause early failure.

Cage and design

• M: machined brass cage.
• J: pressed steel cage (common in some manufacturers' systems).
• TN9 and similar: glass fiber reinforced polyamide cage (manufacturer specific).
• E: optimized internal design with higher load capacity in some ranges.
• K: tapered bore, typically 1:12, for mounting on an adapter or withdrawal sleeve.

Precision

Precision classes such as P6, P5 and P4 indicate tighter tolerances than normal. Machine tool spindles often use high precision angular contact bearings with additional suffixes for contact angle and preload. Spindle bearings are covered in more detail in our article on CNC spindle parts.

Tip: When a suffix is unfamiliar, record it exactly as printed and include the manufacturer name. The same letters can mean different things at different manufacturers.

When the marking is missing

Worn or ground off markings are common on bearings removed from old machines. In that case, measure the bearing:

1. Bore diameter (d): measure the inner ring bore at several points with a caliper or bore gauge.
2. Outside diameter (D): measure the outer ring.
3. Width (B or T): measure the ring width; for tapered bearings, record the total width.
4. Type: note whether the rolling elements are balls, cylindrical, tapered or spherical rollers, and how many rows there are.
5. Seals and cage: note shields, seals and cage material.

Compare the dimensions with a manufacturer catalog. Dimensions that match no standard metric size may indicate an inch series or special bearing; then the machine's parts list or builder may be the only reliable source.

Interchangeability between manufacturers

Basic designations are generally interchangeable between major manufacturers, so a 6205 from one brand fits where a 6205 from another brand was used. Suffixes need closer attention. Seal types, cage materials, clearance and precision should be cross-referenced carefully, not assumed. Our guide on cross-referencing part numbers describes how to do this systematically. If the exact variant is hard to find locally, a sourcing agency such as LiteHard can search distributors and stock holders for the full designation.

What to send with a bearing request

To get an accurate quote quickly, include:

• The complete designation, including prefix and all suffixes, and the brand.
• Photos of the markings on both sides of the bearing.
• Measured dimensions if the marking is unclear.
• The quantity and whether an equivalent brand is acceptable.

Key takeaways

• A bearing designation consists of an optional prefix, a basic designation and optional suffixes.
• The basic designation gives type, dimension series and bore; for codes 04 and above, bore equals code times 5.
• Suffixes define seals, clearance, cage and precision, and they are often manufacturer specific.
• When markings are missing, measure bore, outside diameter and width and identify the bearing type.
• Always send the full designation and photos when requesting a replacement.