A buyer who asks "do you have 6205?" has already given you the three dimensions. Most sales teams answer with a price and a photo; the ones who answer with 25 × 52 × 15 mm, the seal type and the clearance class get the order, because they just proved they know what bearing numbers mean.
A bearing designation is a dimension code, not a product name. Under ISO 15, any manufacturer's 6205 is 25 mm bore, 52 mm outside diameter, 15 mm width. That is the whole reason a machine builder in Ohio can order from a supplier in Ningbo without sending a drawing.
Bearing Numbers Decoded: The Table
The single-row deep groove ball bearing families cover most of what crosses an export desk. Bore, OD and width are in millimetres.
| Designation | Bore d | OD D | Width B | Series character |
|---|---|---|---|---|
| 6200 | 10 | 30 | 9 | Light (02) |
| 6201 | 12 | 32 | 10 | Light (02) |
| 6202 | 15 | 35 | 11 | Light (02) |
| 6203 | 17 | 40 | 12 | Light (02) |
| 6204 | 20 | 47 | 14 | Light (02) |
| 6205 | 25 | 52 | 15 | Light (02) |
| 6206 | 30 | 62 | 16 | Light (02) |
| 6207 | 35 | 72 | 17 | Light (02) |
| 6208 | 40 | 80 | 18 | Light (02) |
| 6305 | 25 | 62 | 17 | Medium (03) |
| 6306 | 30 | 72 | 19 | Medium (03) |
| 6405 | 25 | 80 | 21 | Heavy (04) |
Read the last three rows against 6205. Same 25 mm shaft, three different outer envelopes: 52, 62 and 80 mm OD. That is the point of the dimension series — the shaft is fixed by the machine, the load capacity is chosen by the housing.
How to Read Any Bearing Number in Four Steps
Step 1: The first digit is the bearing type
6 is a single-row deep groove ball bearing. 7 is angular contact, 3 is double-row angular contact, 2 is spherical roller or self-aligning ball, 1 is self-aligning ball, N/NU/NJ prefixes are cylindrical roller, and 32/303-style four-digit numbers are tapered roller. The type digit tells the buyer's engineer what loads the bearing can take, not how big it is.
Step 2: The next digit(s) are the dimension series
In 6205, the "2" is the dimension series — width series 0 combined with diameter series 2, usually written 02 and called the light series. 63xx is series 03, medium; 64xx is 04, heavy. Higher series means a bigger OD and more load capacity on the same bore.
Step 3: The last two digits are the bore code
This is where people guess wrong. From 04 upward the bore code is simply the number multiplied by 5. Below that, four codes are arbitrary and must be memorised.
| Bore code | Bore diameter |
|---|---|
| 00 | 10 mm |
| 01 | 12 mm |
| 02 | 15 mm |
| 03 | 17 mm |
| 04 | 20 mm |
| 05 | 25 mm |
| 08 | 40 mm |
| 12 | 60 mm |
| 20 | 100 mm |
So 6205 is bore code 05 → 25 mm. And 6202 is not 2 mm; it is 15 mm. That one substitution has shipped more wrong bearings than any other single mistake in the trade.
Step 4: The suffix carries everything the number cannot
| Suffix | Meaning | Why the buyer cares |
|---|---|---|
| ZZ or 2Z | Metal shields, both sides | Non-contact, low friction, keeps out coarse debris |
| 2RS / 2RS1 | Contact rubber seals, both sides | Better sealing, more drag, lower max speed |
| C3 | Radial internal clearance greater than normal | Needed for interference fits or hot running |
| C2 | Clearance less than normal | Precision, low-vibration applications |
| /P6, /P5 | Tolerance class per ISO 492 | Tighter dimensional and running accuracy |
| /HT, /VT | High-temperature grease, alternate grease | Operating temperature range |
A designation without a suffix describes an open bearing at normal clearance in the standard tolerance class. If your product is sealed, or C3, or anything other than normal, and you leave it off the quotation, you have quoted a different bearing from the one in the box.
Where This Goes Wrong on Export Orders
The buyer sends only the number. 6205 alone does not say sealed or open, C3 or normal, chrome steel or stainless. Reply with the full designation you intend to ship — "6205-2RS1/C3" — and ask for confirmation. That single line prevents the most common bearing dispute there is.
The tolerance class is assumed. Dimensional and running accuracy classes come from ISO 492, and the normal class is not a marketing claim, it is a numeric limit. If your buyer's application needs P6, they will say P6; if they say nothing and you supply Normal, both of you are correct until an inspection report says otherwise. Put the class on the quotation.
Load ratings get quoted without a source. A 6205 open bearing typically carries a dynamic load rating around 14.0 kN and a static rating around 7.8 kN, but ratings vary by manufacturer and by internal design. Quote your own tested figures and say whose they are.
The photo shows a bearing, not the bearing. A stock image of a shiny bearing with "6205" typed beside it tells the buyer nothing they could not read from the part number. What earns trust is a dimensioned view — bore, OD, width and chamfer called out on the actual part, in a real industrial spec diagram. This is the same discipline that fastener and pipe listings need; metric vs imperial fastener threads and pipe and fitting dimensions cover the two neighbouring families where a designation also hides three dimensions.
A practical tip on making those drawings: whatever tool you use should take dimensions from the measured part and lock them to the image, not from a hand-drawn arrow that gets nudged during a catalogue redesign. Tools that generate a product image with AI are the wrong instrument here — they can render a convincing bearing and print a bore value nobody measured, and in a bearing catalogue a plausible-looking wrong number is a returned container.
What Belongs on a Bearing Listing
- Full designation including prefix and every suffix (e.g. 6205-2RS1/C3)
- Bore, OD and width in mm, stated separately from the designation
- Bearing type in words, not just the type digit
- Seal or shield type, and whether it is contact or non-contact
- Internal clearance class (C2 / Normal / C3 / C4)
- Tolerance class per ISO 492 (Normal / P6 / P5)
- Dynamic and static load ratings, with the standard they were derived under
- Limiting speed for grease and for oil
- Material and cage type (chrome steel, stainless, steel or polyamide cage)
- A dimensioned drawing showing d, D, B and chamfer r
Ten lines. A buyer who reads them does not send a technical enquiry, and a buyer who never has to send a technical enquiry usually reorders.
FAQ
What do bearing numbers mean?
They encode dimensions and type. The first digit is the bearing type, the next is the dimension series, and the last two are a bore code — from 04 upward, bore code × 5 = bore in millimetres. So 6205 is a single-row deep groove ball bearing, light series, 25 mm bore.
What size is a 6205 bearing?
25 mm bore, 52 mm outside diameter, 15 mm width. These boundary dimensions are fixed by ISO 15, so a 6205 from any compliant manufacturer fits the same housing and shaft.
What is the difference between 6205 and 6305?
Both have a 25 mm bore. The 6305 is the medium series: 62 mm OD and 17 mm wide against the 6205's 52 mm and 15 mm, giving it a higher load rating for the same shaft. Choose by housing space and load, not by price alone.
What does 2RS mean on a bearing?
Contact rubber seals on both sides. It seals better than a shielded (ZZ) bearing but adds friction and lowers the limiting speed. 2RS and ZZ are not interchangeable in a quotation even though they share a designation prefix.
What does C3 clearance mean?
Radial internal clearance greater than the normal class, specified for bearings that will run hot or be fitted with a heavy interference fit, where thermal expansion would otherwise preload the bearing. C3 is a different product from the same number without a suffix — always state it.