Bearings
A rolling bearing is bought by a number that already contains its dimensions. 6204 means 20 mm bore, 47 mm outside diameter, 14 mm width — anywhere in the world, from any works. This sub-library starts with the three most widely used deep groove ball bearing series and the 63 designations they share.
What these pages containand what they deliberately leave out
What the designation says. The number is three fields, not one. The first digit is the type — 6 is a single-row deep groove ball bearing. The second digit is the diameter series, which sets how much outside diameter and width the bearing gets for a given bore: 0 is extra-light, 2 is light, 3 is medium, 4 is heavy. The last two digits are the bore code. For 00, 01, 02 and 03 the bore is 10, 12, 15 and 17 mm — special cases. From 04 upwards the code multiplies by five, so 04 is a 20 mm bore and 20 is a 100 mm bore. Read that way, 6204 unpacks to: single-row deep groove ball bearing, light series, 20 mm bore.
The bore code is why one number can replace a drawing. Because the code and the bore are locked together by rule, a buyer who says "6205" has already specified the shaft seat and the housing bore. The catch runs the other way too: two bearings with the same bore are not interchangeable unless the outside diameter and width match as well. 6005, 6205 and 6305 all take a 25 mm shaft and all three need a different housing — 47, 52 and 62 mm respectively. That is the whole reason the diameter series exists: the shaft is fixed by the machine, the bearing is chosen from the space left around it.
Boundary dimensions are standard. Ratings are not. The dimensions on these pages come from ISO 15, which lays out the preferred boundary dimensions for radial bearings and is why every maker's 6204 is the same size. Load ratings and limiting speeds are a different kind of number: ISO 281 defines how a dynamic rating is *calculated*, not what it equals, and the answer depends on internal geometry — ball diameter, how many balls there are, raceway conformity — which ISO 15 deliberately does not fix. Published catalogue values for one and the same designation differ between makes by several percent at the sizes in this batch. So no load rating and no limiting speed appears on any page here. See "What is deliberately not published" below.
A suffix is not part of the size. 6204-2RS and 6204-ZZ have exactly the same bore, outside diameter and width as a plain 6204; the suffix changes the sealing, the clearance group or the tolerance class, none of which the boundary dimension plan has anything to say about. Order by the base designation for size, then add the suffix for the environment.
What is in this first batch, and what is not. 63 designations: the 6000, 6200 and 6300 series, 21 bores each, 10 mm to 100 mm, all to ISO 15. The roadmap below lists what the next batches add — other diameter series, other bearing types, and the standard pages these pages currently cite as plain text.
How to read a designationthree fields, not one number
| Bore code | Bore d | Rule | Example |
|---|---|---|---|
| 00 | 10 mm | special case | 6200 → 10 mm bore |
| 01 | 12 mm | special case | 6201 → 12 mm bore |
| 02 | 15 mm | special case | 6202 → 15 mm bore |
| 03 | 17 mm | special case | 6203 → 17 mm bore |
| 04 and above | code × 5 | 04 → 20 mm, 20 → 100 mm | 6204 → 20 mm bore |
Codes 00 to 03 are the four exceptions to the rule; every code from 04 up is simply multiplied by five. That is why 6204 is a 20 mm bore and 6205 a 25 mm — and why the bore can be read straight off the number without a table.
Bearing size chart21 bores × 3 series, mm
Each cell is outside diameter × width in millimetres, and links to the full page for that designation. Reading down a column walks one series through its bore range; reading across a row is the choice that has to be made once the shaft diameter is fixed — same bore, larger housing, more load capacity. All values are ISO 15 boundary dimensions.
The standards these pages rest onand which number each one governs
| Standard | Governs | Title | Why it matters here |
|---|---|---|---|
| ISO 15 | Bore, outside diameter, width and the minimum chamfer | Rolling bearings — Radial bearings — Boundary dimensions, general plan | The source of every dimension on these pages. The chamfer value it gives is a minimum (r s min) — the matching maximum single chamfer dimension is in ISO 582, which is why the dimension is labelled "min" and not stated as an equality. |
| ISO 492 | Tolerance classes (Normal, 6, 5, 4, 2) | Rolling bearings — Radial bearings — Geometrical product specification and tolerance values | Defines the permissible deviation of the mean bore and mean outside diameter for each class. The class names differ between systems and mean the same thing: Normal is P0 in the DIN scheme, ABEC-1 in the AFBMA scheme and Class 0 in JIS, and 6 / 5 / 4 / 2 map onto P6–P2, ABEC-3–9 and JIS 6–2 respectively. No bearing in this batch is a precision class — they are all Normal — and the numerical limits are not reproduced here. |
| ISO 5753-1 | Radial internal clearance groups C2, CN, C3, C4, C5 | Rolling bearings — Internal clearance — Part 1: Radial internal clearance for radial bearings | The source of the clearance table on each page. Those are pre-mounting values: an interference fit on the shaft and a temperature difference between the rings both reduce the running clearance, which is exactly why the looser groups exist. |
| ISO 582 | The maximum single chamfer dimension | Rolling bearings — Chamfer dimension limits | Completes the chamfer definition: ISO 15 gives the minimum, ISO 582 the matching maximum. Both matter when the bearing sits against a shoulder. |
| ISO 281 | How a load rating is calculated — not what it equals | Rolling bearings — Dynamic load ratings and rating life | Cited here for the opposite reason to the others: it is the standard that explains why no load rating is published on these pages. It defines the calculation and the life equation, while the inputs that feed it come from the individual bearing's internal design. |
None of these has its own page yet. The standards module is built around fastener product standards and fastener mechanical-property standards, and a bearing standard is a different kind of document — it is cited here as text rather than linked.
Suffixes do not change the sizewhat the letters after the number mean
| Suffix | Meaning | Effect |
|---|---|---|
| (none) | Open bearing — no shield, no seal | Lowest friction and highest limiting speed; needs relubrication and a clean environment |
| Z / ZZ | One / two metal shields, non-contact | Keeps coarse dirt out, does not seal against liquid; lower friction than a contact seal |
| 2RS | Two contact rubber seals | Seals against dust and moisture, usually greased for life; more friction, lower limiting speed |
| 2RZ / 2RU | Two non-contact rubber seals | Between a shield and a contact seal: better protection than ZZ, less friction than 2RS |
| C2 / C3 / C4 / C5 | Radial internal clearance group, tighter or looser than normal | Affects the fit and the running clearance only — the clearance ranges are tabulated below |
| P6 / P5 / P4 / P2 | Tolerance class above Normal | Tighter bore and outside diameter limits and lower runout; for spindles and precision work |
None of these suffixes changes the bore, outside diameter or width. A 6204-2RS and a 6204 have identical boundary dimensions; the suffix changes the environment the bearing will survive in, not the shaft or the housing it fits. Note also that the clearance codes sit in the same place as the sealing codes and mean something entirely different — C3 is not a seal.
What is deliberately not publishedwhy there is no load rating here
No load rating, no limiting speed and no mass appears on this page. Those are catalogue values rather than standard values: ISO 281 defines how a dynamic rating is calculated, not what it comes out as, and the result depends on internal geometry — ball diameter, ball complement, raceway conformity — that ISO 15 does not fix. Published catalogue figures for one and the same designation differ between makes by several percent at these sizes, and limiting speed additionally depends on lubrication and on whether the bearing is open, shielded or sealed. Publishing any single figure here would dress a catalogue entry up as a property of the designation. Take the rating from the catalogue of the bearing you actually buy.
The dimensions above are a different matter, and they are the reason a designation is worth anything: bore, outside diameter, width and the chamfer minimum are fixed by ISO 15, so every maker's bearing of this designation fits the same shaft and the same housing.
Frequently asked questionsreading a bearing designation
What do the numbers in a bearing designation mean?
6204 is three fields: 6 is the type (single-row deep groove ball bearing), 2 is the diameter series (0 extra-light, 2 light, 3 medium, 4 heavy), and 04 is the bore code. Bore codes 00, 01, 02 and 03 are 10, 12, 15 and 17 mm; from 04 upwards the code is multiplied by five, so 04 is 20 mm. 6204 is therefore a 20 mm bore, light series deep groove ball bearing.
Is a 6204 from one manufacturer the same size as another's?
Yes. The boundary dimensions — bore, outside diameter, width and the minimum chamfer — are fixed by ISO 15, so any compliant 6204 is 20 × 47 × 14 mm and fits the same shaft and housing regardless of who made it. What is not the same between makes is the load rating and the limiting speed, which is why neither is published on these pages.
Why is there no load rating on these pages?
Because a load rating is a catalogue value, not a standard value. ISO 281 defines the calculation; the number it produces depends on the internal geometry of the specific bearing, which ISO 15 does not constrain. Two catalogues for the same 6205 disagree by several percent, so publishing one maker's figure as if it were a property of the designation would be presenting a catalogue entry as a standard. Take the rating from the catalogue of the bearing you actually buy.
Does a 2RS or ZZ suffix change the dimensions?
No. Seals and shields change the sealing, the friction and the limiting speed — never the boundary dimensions. A 6204-2RS and a 6204 have the same 20 mm bore, 47 mm outside diameter and 14 mm width.
Which clearance group should I order?
CN (the normal group) is the default and usually is not marked on the bearing at all. C3 — looser — is the common choice where the inner ring is an interference fit on the shaft, in electric motors, and wherever the inner ring runs hotter than the outer ring, because both effects take up clearance. C2 is tighter, C4 and C5 looser still. The ranges are on each page from ISO 5753-1; they are pre-mounting values, and mounting and temperature reduce them.