How to read bearing numbers: designation system, bore codes and suffixes

Updated 2026-09-24

A stamped bearing number like 6205-2RS1/C3 or NU2310 E C3 is not a random part code — it is a compressed description of the bearing’s type, size and options. Reading it takes about ten seconds once the structure is known, and it prevents the most common purchasing error: ordering by base number alone and receiving a bearing that fits but performs differently.

The four parts of a designation

[Type/series prefix] [Bore code] [Suffix block]
        62                05        -2RS1 / C3

1. Type indicator and dimension series — what kind of rolling elements and how heavy the ring section is.
2. Bore code — the shaft diameter.
3. Seals/shields — the external barrier.
4. Clearance, cage, precision and internal design — the operating-character suffixes.

Step 1: the type digit and dimension series

The leading digit identifies the bearing family:

The digit immediately before the bore code is the dimension series: the second digit is the diameter series (how heavy the outer section is), an optional first digit the width series. Within one bore, a 6305 is bigger and heavier-rated than a 6205, which is bigger than a 6005. Thin-section 718xx/719xx angular-contact bearings carry the extra digit. Compare whole families on the 25 mm bore index to see how the same shaft carries four section weights.

Step 2: the bore code (the part everyone gets wrong once)

From code 04 upward, bore in mm = code × 5:

Codes 00–03 follow the exception table: 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm. So a 6201 has a 12 mm bore — applying ×5 there is the classic mistake. Bores above 200 mm, tapered (K) variants and inch-series bearings are coded directly (e.g. 230/500 = 500 mm bore).

Step 3: seals and shields

The full comparison is in 6205 vs 6205-2RS.

Step 4: clearance, cage and precision suffixes

• C2 < CN < C3 < C4 — radial internal clearance from tighter to looser than normal; CN is rarely printed. See the clearance-class guide for how fits and heat consume play.
• K — 1:12 tapered bore on an adapter sleeve (roller bearings).
• E — reinforced roller complement, higher C rating in the same envelope.
• J / M / P-type cage codes — stamped steel, machined brass, polymer cages.
• P6 / P5 / P4 — progressively tighter tolerance classes for precision spindles.
• Angular-contact suffixes encode contact angle and pairing: C ≈ 40°, E/A5 ≈ 25°, with DB/DF/DT mounting arrangements — see paired angular-contact bearings.
• Cylindrical roller ring designs NU/NJ/NUP are prefixes, not suffixes, and decide axial location — see NU vs NJ vs NUP.

Practical reading: three worked examples

• 6205-2RS1/C3 — deep-groove, light series 02, 25 mm bore, two contact seals, C3 clearance.
• 7205 BECBP — angular-contact, light series, 25 mm bore, 40° contact angle, universal pairing — verify the brand-specific pairing letters in the catalogue.
• NU2310 E C3 — cylindrical roller, axially free NU design, medium-wide series 23, 50 mm bore (110×40 mm envelope), reinforced roller set, C3 clearance.

The one rule that prevents most ordering errors

Never order on the base number across brands without decoding the suffixes and checking the load rating. The base number guarantees the ISO envelope — that is why the 25×52×15 interchange table works — but seals, clearance, cage and internal geometry decide whether the replacement lives. Brand pages (SKF, NSK) show the exact catalogued rows; the cross reference tool grades each proposed equivalent full / partial / verify.