Spindle Bearing Cross-Reference: Translating FAG, SKF, NSK and Koyo Super-Precision Designations
Someone in your plant hands you a spindle bearing and the number reads B7207-C-T-P4S-UL. The catalogue you have open is SKF. Nothing in it looks remotely like that string.
The bearing you want is 7207 CDGA/P4A. Same bore, same outside diameter, same width, same contact angle, same preload class. Different manufacturer, completely different grammar for saying so.
This is the single most common thing people fail to find on Partmatch. We looked at our missed-search log and found 16,956 separate visitors who searched two or more different brand spellings of the same base bearing, usually within a few minutes of each other. They were not browsing. They were translating.
So here is the translation.
Why super-precision numbers look nothing like each other
Standard bearing numbering is roughly harmonised. A 6205 is a 6205 whoever makes it, because the base designation follows ISO 15. Super-precision spindle bearings are where that harmony breaks down.
Every manufacturer builds their designation from the same underlying decisions -- bore size, contact angle, cage material, tolerance class, preload, whether it is a matched set -- but each encodes those decisions in their own notation, in their own order, with their own letters. FAG puts the tolerance class near the end and prefixes the whole thing with B. NSK compresses cage and seal and preload into one run of letters. SKF separates the base from the suffix with a slash.
The information content is close to identical. Only the spelling differs.
The same bearing, four ways
Take a 25 mm bore, 15 degree contact angle, phenolic cage, ABEC-7 tolerance, universal light preload spindle bearing. Here is how the major manufacturers write it:
| Manufacturer | Designation |
|---|---|
| FAG | B7205-C-T-P4S-UL |
| SKF | 7205 CD/GA/P4A |
| NSK | 7205CTYSULP4 |
| RHP | 7205-CT-SUL-P4 |
| KOYO | 7205CPAGLFTP4 |
Every one of those is the same physical part. If you have been handed one and can only source another, that is a straight swap.
Reading the FAG form
FAG super-precision numbers are the ones that look most alien, and they are actually the most systematic once you see the fields. B7207-C-T-P4S-UL breaks down as:
| Field | Meaning |
|---|---|
| B | Spindle bearing series |
| 72 | Dimension series |
| 07 | Bore code, 07 times 5 equals 35 mm |
| C | 15 degree contact angle |
| T | Textile laminated phenolic resin cage, outer ring guided |
| P4S | Boundary dimensions ISO 4 / ABEC-7, running accuracy ISO 2 / ABEC-9 |
| UL | Universal, light preload |
The variants you will run into most:
| Code | Meaning |
|---|---|
| C | 15 degree contact angle |
| E | 25 degree contact angle |
| T | Phenolic cage |
| 2RSD | Two rubber seals |
| HC | Ceramic balls, hybrid |
| P4S | Restricted tolerances, ABEC-7 boundary |
| UL | Universal, light preload |
| UM | Universal, medium preload |
| DUL | Duplex universal, light preload |
UL and DUL are the pair that causes ordering mistakes. UL is a single bearing that can be universally matched. DUL is a duplex set, meaning two bearings supplied and matched as a pair. Ordering one when you needed the other is a phone call you would rather not make.
Reading the NSK form
NSK compresses more into a single run. 7205CTYSULP4 reads as:
| Field | Meaning |
|---|---|
| 72 | Dimension series |
| 05 | Bore code, 25 mm |
| C | 15 degree contact angle |
| TYN or TY | Polyamide cage |
| T or TR | Phenolic cage |
| SU | Universal, single |
| L | Light preload |
| P4 | ISO Class 4, ABEC-7 |
The NSK codes worth knowing:
| Code | Meaning |
|---|---|
| A5 | 30 degree contact angle |
| C | 15 degree contact angle |
| TYN | Polyamide cage |
| TR | Phenolic cage, replaces older T |
| SU | Universal single |
| DU | Duplex universal |
| EL / L / M / H | Extra light / light / medium / heavy preload |
| P4 | ISO Class 4 |
| P4Y | NSK special class, tighter bore and OD control than P4 |
| P2 | ISO Class 2, ABEC-9 |
P4Y is worth flagging because it is NSK-specific and does not have a direct equivalent elsewhere. NSK's own literature describes it as tighter bore and outside diameter control than standard P4, introduced to make matching sets easier. If a print calls for P4Y and you substitute a competitor's P4, you have not matched the tolerance the designer specified.
Reading the SKF form
SKF splits base from suffix with a slash, and the suffix stacks left to right. S7016 ACE/HCP4ADGA:
| Field | Meaning |
|---|---|
| S | Prefix |
| 70 | Dimension series |
| 16 | Bore code, 80 mm |
| AC | 25 degree contact angle |
| E | Optimised internal design |
| HC | Ceramic balls, hybrid |
| P4A | Super-precision tolerance class |
| DG | Universal matching |
| A | Light preload |
SKF uses A, B, C as the trailing preload letter -- light, moderate, heavy -- which is the same scale as their standard GA, GB, GC universal matching codes. Once you notice that, HCP4ADGA stops being one impenetrable code and becomes four stacked decisions.
The fields that actually have to match
When you are checking whether a substitution is real, these are the ones that change the part:
- Contact angle. FAG
Cand NSKCare both 15 degrees. FAGEis 25 degrees, NSKA5is 30 degrees, SKFACis 25 andAis 30. Getting this wrong changes the load capacity of the whole arrangement, not just the bearing. - Preload. Light, medium and heavy are not interchangeable. A spindle designed around light preload will run hot on heavy.
- Tolerance class. P4 / P4S / ABEC-7 are broadly equivalent across brands. P2 and ABEC-9 are a step tighter. NSK's P4Y sits between and is proprietary.
- Single versus duplex. FAG
ULagainstDUL, NSKSUagainstDU. One bearing or two. - Cage material. Phenolic and polyamide have different temperature and speed limits.
- Ceramic or steel balls. FAG
HC, SKFHC, NSKHorSN24. Hybrid bearings run cooler and faster and cost considerably more.
Furthermore, the arrangement codes are a separate layer on top. Back-to-back, face-to-face and tandem are DB, DF and DT at SKF, and the equivalent letters differ elsewhere. A matched set is not a part you can swap one half of.
A worked example
B7205-C-T-P4S-UL from FAG. Distributor cross-references list the following as equivalents:
| Manufacturer | Designation |
|---|---|
| SKF | 7205-CD-GA-P4A |
| NSK | 7205CTYSULP4 |
| RHP | 7205CTRSULP4 |
| KOYO | 7205CPAGLFTP4 |
| FAFNIR | 2MM205WI-CRUL |
Read across and the fields line up. Every one is a 25 mm bore, 15 degree contact angle, ABEC-7, universally matchable single bearing with light preload. The letters that carry "light preload" are UL at FAG, GA at SKF, SUL at NSK, and GL inside the Koyo string. Same decision, four spellings.
Where this gets genuinely hard
Two honest caveats, because a translation table that pretends to be complete is worse than one that admits its edges.
The first is proprietary classes. NSK's P4Y is the clearest example, but every manufacturer has designations that exist because they wanted a specification the others do not offer. Those do not translate cleanly and should not be forced.
The second is that a cross-reference at the designation level is not the same as an engineering approval. Two bearings with matching fields will fit the same housing and shaft and behave similarly. Whether they are approved for your particular spindle at your particular speed and load is a question for the manufacturer or the machine builder, not for a lookup table.
Lastly, the sealed variants complicate things. FAG 2RSD and NSK V1V are both sealed executions, but sealing changes speed limits, and a sealed bearing substituted for an open one in an oil-air lubricated spindle is a different animal entirely.
Looking one up
If you have a designation in hand and want the equivalents rather than the rules, search it on Partmatch. We hold cross-reference data across the 72xx and 70xx super-precision range, and we mark how confident we are in each match rather than presenting everything as verified.