How to Read Bearing Numbers
A bearing number looks arbitrary until you know where to split it. Take 6205-2RS C3. That is three separate pieces of information: what kind of bearing it is, how big it is, and how it has been built. Read them in order and the number explains itself.
The Anatomy of a Number
| Part | Example | Tells you |
|---|---|---|
| First digit | 6205 | Bearing type |
| Second digit | 6205 | Dimension series |
| Last two digits | 6205 | Bore size |
| Suffix | 6205-2RS C3 | Seals, clearance, variations |
First Digit: The Type
The 6 at the start of a conventional four-digit designation such as 6205 identifies a single-row deep groove ball bearing. Other families use different designation systems. A leading digit alone is insufficient: identify the complete series and check the manufacturer’s catalogue.
Numbers beginning 16 are also deep groove, in an especially narrow form. For the miniature 608 designation, the bore is 8 mm. Do not apply that shortcut to every three-digit number; verify the miniature series in the maker’s catalogue.
Second Digit: The Dimension Series
This sets how much bearing surrounds the bore. Higher generally means a bigger outer diameter, more width, and more load capacity for the same shaft.
- 68 — extra thin section
- 69 — thin section
- 60 — extra light
- 62 — light, and the most commonly stocked
- 63 — medium
- 64 — heavy
Our bearing size guide shows five series at the same 10 mm bore side by side, which makes the difference obvious.
Last Two Digits: The Bore
Four codes are exceptions — 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm. For conventional two-digit bore codes 04 through 96, multiply the code by five. Special bore sizes, slash designations and miniature bearings need their own catalogue rules. So 6204 is 20 mm, 6208 is 40 mm, and 6820 is 100 mm.
Suffixes
Everything after the base number describes how the bearing has been built. Suffix meanings are manufacturer-specific. The following are common conventions, not a universal translation table; confirm the full designation in the relevant manufacturer catalogue.
| Suffix | Meaning |
|---|---|
| Z / ZZ / 2Z | Metal shield on one side / both sides |
| RS / 2RS / RS1 | Seal labels whose precise design and side count must be checked in the maker’s catalogue |
| C2 | Internal clearance tighter than normal |
| CN | Normal clearance — usually left off the number entirely |
| C3 | Clearance greater than normal; common in electric motors and where the bearing runs hot |
| C4 / C5 | Greater still |
| E | Manufacturer- and bearing-family-specific design code; consult the exact catalogue |
| P5 / P6 | Tighter dimensional tolerance than standard |
Suffixes combine, so 6205-2RS C3 is a light-series bearing with a 25 mm bore, rubber seals both sides, and increased internal clearance.
Prefixes
Letters in front are manufacturer-specific and do not follow a shared standard. They usually mark a material or a product line — stainless steel, a ceramic hybrid, or a particular grade. Because they are not standardised, prefixes and suffixes must both be checked against that manufacturer’s own catalogue rather than assumed.
Manufacturer-Specific Examples and Sources
NSK uses Z/ZZ for shields, DU/DDU for contact seals and V/VV for non-contact seals. These are NSK examples, not automatic translations to SKF or other brands. Preserve additional clearance, cage and precision codes when identifying a product.
Source: NSK Bearing and Linear Replacement Guide, bearing identification section. Its bore table distinguishes 00-03, conventional 04-96 codes and special slash-designated bores. Check the current exact product record before ordering.
Worked Examples
| Number | Reads as |
|---|---|
| 6000 | Deep groove, extra light series, 10 mm bore |
| 6204-2Z | Deep groove, light series, 20 mm bore, shielded both sides |
| 6305 C3 | Deep groove, medium series, 25 mm bore, increased clearance |
| 6900-2RS | Deep groove, thin section, 10 mm bore, sealed both sides |
| 6820 | Deep groove, extra thin section, 100 mm bore |
Not sure whether you need shields or seals? See 2RS vs ZZ seals. To find dimension candidates and source status, search the full marking in the cross reference database.
Related: 6205 Bearing Selection and Manufacturer Evidence — Review manufacturer dimension records, full designations and the checks needed before comparing replacements.
Real-world example: The 6304 follows this exact naming pattern — 6 (single-row deep groove) + 3 (medium series) + 04 (20mm bore). Compare to the 6205 for how the same system works with different sizes.