A bearing on a conveyor fails, and the stores team finds three boxes on the shelf that all start with the same four digits. One is shielded, one is sealed, one has a larger internal clearance. Only one of them is what the machine was built with. The same happens with V-belts that share a section but not a length system, and with chains that share a pitch but not a series.
Power transmission parts are the most standardised items in a factory’s consumables list, which is exactly why they are so often bought wrongly: the shared part of the code makes different parts look interchangeable. This guide covers how to read the codes, what is shared between makers, and what to check before fitting an equivalent.
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Bearings: the basic number is shared, the suffix is the maker’s
A rolling bearing’s basic number tells you its type, dimension series and bore, and for standard sizes it is the same across the major makers. The suffixes for seals, shields, clearance and precision are what differ, and they are usually the reason a bearing fails early.
Bearing numbers are made of a basic number followed by supplementary codes. One maker’s catalogue explains the structure with this example: 6205 ZZ C3.
| Part | Example | Meaning |
|---|---|---|
| Type code | 6 | Deep groove ball bearing |
| Dimension series | 2 | Diameter series 2 |
| Bore code | 05 | Nominal bore diameter 25 mm |
| Shield or seal | ZZ | Steel shield on both sides (in that maker’s codes) |
| Internal clearance | C3 | Radial internal clearance larger than normal |
The bore code has a fixed pattern for most metric sizes. Codes 00, 01, 02 and 03 mean 10, 12, 15 and 17 mm. From 04 upwards, the code multiplied by five gives the bore in millimetres: 05 is 25 mm, 08 is 40 mm, 20 is 100 mm. Sizes that do not fit the pattern are written with a slash, such as /22 for a 22 mm bore.
Why the basic number is interchangeable
The boundary dimensions of radial bearings, meaning bore, outside diameter, width and chamfer, are set out in ISO 15:2017, Rolling bearings — Radial bearings — Boundary dimensions, general plan. That is why a 6205 from one maker has the same 25 mm bore and 52 mm outside diameter as a 6205 from another.
Why the suffix is not
The suffix codes are the makers’ own. The same feature may be written differently by different makers, and the same letters may mean different things. Before accepting a bearing from another maker, translate the suffix, not just the basic number:
| Feature | What to confirm | Why it matters |
|---|---|---|
| Shields or seals | Open, shielded or contact or non-contact seal, one or both sides | Contamination and grease retention; speed limit differs |
| Internal clearance | Normal, C3, C4 or other | Shaft fit and temperature; wrong clearance can overheat or run loose |
| Precision class | Normal, or a higher class such as Class 6 or Class 5 | Spindles and precision machines need the class specified |
| Cage | Pressed steel, machined brass, polyamide | Speed, temperature, vibration |
| Grease | Maker’s standard or a specified grease | High or low temperature, food-area use |
| Snap ring groove | With or without | The housing may depend on it |
Makers whose bearings buyers commonly specify by number include SKF, Schaeffler (INA and FAG brands), NSK, NTN, JTEKT (Koyo brand), NACHI and Timken. Each publishes its own catalogue with its own suffix codes. These are examples of brands buyers specify by number. Naming them does not imply any relationship with, or authorisation from, these makers.
V-belts: section first, then the length system
A V-belt is specified by its section and its length, but makers state length in different systems, so record both the section and which length the number refers to before you accept another maker’s belt.
Classical and narrow V-belts are covered by ISO 4184:2025, Belt drives — Classical and narrow V-belts — Lengths in datum system. Its scope covers classical sections Y, Z, A, B, C, D and E, and narrow sections SPZ, SPA, SPB and SPC.
The trap is the length. A belt can be described by datum length, inside length or outside length, and makers’ catalogues do not all use the same one on the belt marking. Two belts marked with the same number may differ in actual length if they use different systems. One maker’s catalogue, for example, lists the same classical A-section belt as 710 mm inside length, 740 mm datum length and belt number A 28. All three refer to one belt; mixing them up gives a belt 30 mm too long or too short. For the item list, record:
| Field | Example | Note |
|---|---|---|
| Section | SPA, B | Section letters as in ISO 4184 |
| Length and length system | Datum, inside or outside length | Ask the supplier to state which |
| Construction | Wrapped, raw-edge, cogged | Changes flexibility and the pulley sizes it suits |
| Matched sets | Number of belts run together | Multi-belt drives need matched lengths |
| Maker and code | As printed on the belt | Keep for traceability |
Toothed timing belts, flat belts and poly-V (ribbed) belts are specified by their own profile, pitch, width and length. Many timing belt profiles are makers’ own designs. Record the maker’s full code and do not substitute between profiles that look similar.
Makers whose belts buyers commonly specify include Gates, Bando, Mitsuboshi and Optibelt. As with bearings, these are examples only.
Roller chains: pitch, series and strand count
A roller chain is specified by its pitch, its standard series, the number of strands and the length, and the sprocket must match the same series. Chains of the same nominal pitch from different series do not run on each other’s sprockets reliably.
Short-pitch precision roller chains, bush chains and their sprockets are covered by ISO 606:2015, which sets dimensions, tolerances, length measurement, preloading and minimum tensile and dynamic strength. Bicycle and motorcycle chains are covered by other standards.
For the item list, record:
- the chain number as the maker gives it, and the series it belongs to;
- pitch;
- number of strands (simplex, duplex, triplex);
- length in links or metres, and the connecting link type;
- material or surface treatment (standard, stainless, plated), and any attachments.
The sprocket’s tooth form depends on the chain series. If you change chain series, change the sprockets. Wear also matters: a new chain on worn sprockets wears faster than the old one did. Replacing chain and sprockets together is a common maintenance practice for that reason.
Makers whose chains buyers commonly specify include Tsubaki, Renold and iwis. Again, these are examples only.
💬 Want bearings, belts and chains bought by full code, with the suffix checked before dispatch? We source each line in Vietnam or abroad and match it to your item list. See MRO and factory consumables.
When an equivalent is safe to fit
An equivalent bearing, belt or chain is safe to fit when the standard part of the code matches, every suffix has been translated and matched, and the machine maker has no special requirement for that position.
A short decision table for the maintenance engineer:
| Situation | Usual decision |
|---|---|
| Same basic number, suffixes translated and matched, general machinery | Equivalent acceptable after the engineer checks the translation |
| Precision spindle, high speed or special clearance | Stay with the specified maker and class unless the machine maker approves |
| Machine maker lists its own part number | Ask the machine maker for the component number and any special specification |
| Food or clean area | Confirm grease, seals and any material requirement before substitution |
| Belt with an unclear length system | Measure, or match against the maker’s length table before ordering |
Record each approved equivalent in the item list’s approved-alternatives column, so that the decision is made once. How to build that list for all consumables is set out in MRO supply for factories in Vietnam.
Labels, packaging and traceability
Keep power transmission parts in the maker’s packaging until they are fitted, because the box carries the full code, lot information and, for some makers, a code that can be checked against the maker’s database.
Bearings are among the most copied industrial parts. Some makers print a code on the box that can be checked with their own app, and buying through a channel traceable to the maker remains the main defence. How these checks work, maker by maker, is in avoiding counterfeit bearings and industrial parts.
For receiving:
- check the full code on the box against the order, including every suffix;
- keep the box with the part in stores, not loose on a shelf;
- record the supplier and invoice for every lot;
- for critical positions, photograph the box label before the part is fitted.
If the bearings are for a Japanese machine and must be genuine Japanese parts shipped from Japan, see genuine Japanese industrial parts. If you are combining these lines with parts from other countries, see consolidating Asian suppliers into one shipment.
💬 Need a regular supply of bearings, belts and chains matched to your machines? Send us the item list and the machines they go on. Contact us about factory consumables.
Frequently asked questions
1. Is a 6205 bearing from one maker the same as a 6205 from another?
The basic dimensions are the same, because radial bearing boundary dimensions follow ISO 15. The suffixes for seals, shields, clearance, cage and precision are each maker’s own. Translate and match every suffix before treating them as the same part.
2. How do I read the bore from a bearing number?
For most metric bearings, the last two digits of the basic number are the bore code. Codes 00 to 03 mean 10, 12, 15 and 17 mm. From 04 upwards, multiply by five. Sizes outside the pattern are written with a slash, such as /22.
3. Why does a replacement V-belt with the same number not fit?
Most often because the length is stated in a different system: datum, inside or outside length. Record the section and the length system on the item list, and ask the supplier to confirm which one the number refers to.
4. Can I fit a new chain on old sprockets?
It will run, but a new chain on worn sprockets usually wears faster. Check the sprockets for wear, and make sure they match the chain’s series. Replacing both together is a common maintenance practice.
5. How do I know a bearing is genuine?
Buy through a channel you can trace back to the maker, keep the maker’s packaging, and use the maker’s own verification route where one exists. The checks are set out in our guide to avoiding counterfeit bearings and industrial parts.
Checked on 27 October 2026. Standards are cited by title and edition as listed by standards bodies; confirm the edition your machine maker or market specifies before you rely on it.
Sources: ISO 15:2017, Rolling bearings — Radial bearings — Boundary dimensions, general plan (iso.org/standard/69977.html). ISO 4184:2025, Belt drives — Classical and narrow V-belts — Lengths in datum system (iso.org/standard/88704.html). ISO 606:2015, Short-pitch transmission precision roller and bush chains, attachments and associated chain sprockets (iso.org/standard/61232.html). Bearing number structure, bore codes and the 6205 ZZ C3 example from NTN’s catalogue section “Boundary Dimensions and Bearing Number Codes” (ntnglobal.com). 6205 dimensions from the makers’ product pages.