Take a part number like 6203-2RS C3. A sourcing engineer should read three segments instantly: base model (6203), seal suffix (2RS), clearance group (C3). This guide lists the common suffixes and prefixes — seals, clearance, precision, cages, contact angles — with what each one means and what to double-check when ordering. Organized per GB/T 272 designation rules, ISO 15, and the public conventions of SKF, NSK, NTN, FAG and KOYO. Some codes are vendor-specific; when in doubt, send us the part number and we will decode it against the original catalogue.
1. Seal and shield suffixes (start here)
| Suffix | Meaning | Selection notes |
|---|---|---|
ZZ | Double metal shields | Stamped steel, non-contact. Low friction, high speed; not watertight — needs a clean environment |
2Z | Double metal shields | SKF style, same as ZZ |
Z | Single metal shield | Other side open for relubrication; less protection than ZZ |
2RS | Double contact rubber seals | NBR lip contacts inner ring. Sealed for life, dust + moisture protection; more friction, lower speed limit than ZZ |
2RS1 | Double contact rubber seals | SKF style, same as 2RS |
2RSR | Double contact rubber seals | FAG style, same as 2RS |
DDU | Double contact rubber seals | NSK style, same as 2RS |
LLU | Double contact rubber seals | NTN style, same as 2RS |
RS / RS1 | Single contact seal | Balance of protection and relubrication, for cavities with external shielding |
2RZ | Double non-contact rubber seals | Rubber shroud does not touch the inner ring. Friction close to ZZ, protection close to 2RS — the high-speed + dust compromise |
VV | Double non-contact seals | NSK style, same as 2RZ |
LLB | Double non-contact seals | NTN style, same as 2RZ |
2RU | Double non-contact seals | KOYO style, same as 2RZ |
KRR | Triple-lip agricultural seal + slinger | INA/FAG agricultural code. Extreme mud/water/dust resistance for farm machinery |
KRRB | Triple-lip seal + snap ring | KRR plus locating snap ring on the outer ring |
Same seal, different brands (where replacement mix-ups happen)
| Seal type | SKF | NSK | NTN | FAG | KOYO |
|---|---|---|---|---|---|
| Double metal shield | 2Z | ZZ | ZZ | 2ZR | ZZ |
| Double contact rubber seal | 2RS1 | DDU | LLU | 2RSR | 2RS |
| Double non-contact seal | 2RZ | VV | LLB | 2RSD | 2RU |
Verification point: matching the seal code is only step one of a cross-brand replacement. Two bearings both marked 2RS can differ in lip interference, grease cavity design and factory fill grease. For low-speed applications this rarely matters; for high-speed or high-temperature service, sample-verify before committing to volume.
2. Clearance group suffixes
| Suffix | Meaning | Selection notes |
|---|---|---|
CN | Normal clearance | Default for general conditions, usually unmarked |
C2 | Less than normal | Precision / low-noise orientation; can seize after interference fitting — use with care |
C3 | Greater than normal | The electric motor default. Compensates fit contraction and inner-outer temperature difference |
C4 | Greater than C3 | High-temperature service or heavy interference fits (ovens, hot-air equipment) |
C5 | Greater than C4 | Special high-temperature / large differential, rarely used |
If a customer drawing specifies C3, the buyer understood fits and temperature — never substitute the CN default, the machine will fail on assembly. Conversely, ordinary hand tools run fine on CN; paying for C3 gains nothing. Full explanation in our bearing clearance guide.
3. Precision class suffixes
| Suffix | Meaning | Approx. equivalent | Selection notes |
|---|---|---|---|
P0 | Normal precision | ≈ ABEC-1 | Default for general machinery, usually unmarked |
P6 | Higher grade | ≈ ABEC-3 | Higher-speed or vibration-sensitive equipment |
P5 | Precision grade | ≈ ABEC-5 | Machine tool spindles, precision motors; price steps up visibly |
P4 | High precision | ≈ ABEC-7 | High-speed spindles, precision instruments |
P2 | Ultra precision | ≈ ABEC-9 | Top-tier precision, made to order |
Precision and clearance are two different systems: P5 controls "how accurately it runs", C3 controls "how much play it has". The most common motor combination is P0 + C3. Details in our precision grades guide.
4. Cage suffixes
| Suffix | Meaning | Selection notes |
|---|---|---|
J | Pressed steel cage | Default construction; high strength and impact resistance, slightly lower speed limit than polymer |
M | Machined brass cage | Impact and high-temperature resistant for heavy load / vibration; higher cost |
TN | Nylon cage (PA66) | Low noise, low friction, common in motors; long-term temperature limit around 100 °C |
TN9 | Glass-fibre reinforced nylon (PA66+GF25) | Low noise plus better temperature capability, around 120 °C long-term |
5. Contact angle suffixes (angular contact bearings)
| Suffix | Contact angle | Typical use |
|---|---|---|
C | 15° | High speed, precision spindles (with universal matching) |
AC | 25° | General angular contact, higher axial capacity than C |
B | 40° | Maximum axial load capacity, lower speed limit |
Pairing codes matter as much as the angle: DB (back-to-back), DF (face-to-face), DT (tandem), plus preload classes. A high-precision angular contact bearing ordered without pairing and preload information cannot be mounted correctly — always specify both.
6. Prefixes (the letters before the number)
| Prefix | Meaning |
|---|---|
R | Ring set (rings without balls/cage) in some brand systems |
K | Bearing with cone (tapered bore, 1:12) — e.g. K30205 |
GS / WS | Thrust washer / shaft washer for cylindrical/thrust roller bearings |
F | Flanged outer ring (e.g. F608) — check housing design before ordering |
N (as prefix) | Notch or snap-ring groove in some systems; verify against the brand catalogue |
Prefix conventions vary more between brands than suffixes. For anything beyond the common list above, decode against the specific manufacturer's catalogue — or send it to our engineers.
How to use this decoder when ordering
- Write the full code —
6204-2RS C3, not "6204". Every suffix changes what arrives. - Confirm the brand's own spelling — use the cross-brand seal table above to map SKF / NSK / NTN / FAG / KOYO equivalents.
- Match clearance and fit together — the shaft tolerance class decides how much clearance survives mounting.
- For angular contact: angle + pairing + preload — all three or the assembly will not perform.
FAQ
What does ZZ mean on a bearing?
ZZ means two stamped-steel shields, one on each side. Non-contact, low friction, good speed — but not a seal: it blocks large debris only, and moisture passes through.
What is the difference between 2RS and 2RZ?
2RS seals have rubber lips in contact with the inner ring — full dust and moisture protection, sealed for life, more friction. 2RZ seals do not touch the inner ring — friction close to ZZ with protection close to 2RS, the choice for high-speed dusty applications.
Is DDU the same as 2RS?
Yes in function — DDU is NSK's code for a double contact rubber seal, equivalent to 2RS (SKF 2RS1, NTN LLU, FAG 2RSR).
What does the C3 after a bearing number mean?
C3 means radial internal clearance larger than the normal group. It is the default for electric motors: interference fits and operating temperature reduce clearance, so C3 leaves the right operating clearance.
Do suffixes change the bearing's dimensions?
Normally no — ZZ, 2RS, 2RZ and open variants of the same base number share boundary dimensions. The exceptions are special prefixes (flanged, tapered bore) which change the envelope.
What does M mean in a bearing designation?
M means a machined brass cage — selected for heavy loads, vibration and high temperature, at higher cost than the default pressed steel (J) or nylon (TN) cages.
Related resources
- Bearing Clearance Explained: C2, CN, C3, C4
- Bearing Precision Grades P0 to P5
- 608ZZ vs 608-2RS: Which Seal Fits Your Application?
- 6204 Bearing Guide — suffix meanings applied to one model
- Cross-Reference Tool — map brands to NLHB equivalents