6304 bearing: complete specifications & equivalents
The 6304 is a ISO 15 radial bearing sized 20 x 52 x 15 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 20 mm |
| Outer diameter D | 52 mm |
| Width B | 15 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 16.8 kN |
| Basic static load rating C0 | 7.8 kN |
| Fatigue load limit Pu | 0.335 kN |
| Reference speed (thermal) | 30000 rpm |
| Limiting speed (mechanical) | 19000 rpm |
| Operating temperature | -40 to +150 °C |
| Mass | 140 g |
| Manufacturer designation | SKF 6304 |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-25 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-24
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.
Dimensions in inches & 6300-series range
| Bore d | 0.787 in |
|---|---|
| Outer diameter D | 2.047 in |
| Width B | 0.591 in |
| ISO bore code | 04 |
| Radial section height (D−d)/2 | 16 mm |
| Smallest bore in 6300-series | 2 mm |
| Largest outer diameter in 6300-series | 500 mm |
| Width range across 6300-series | 3–95 mm |
| Bore position in 6300-series (smallest first) | 9 of 40 |
| Bore above smallest 6300-series size | 18 mm |
Mounting, lubrication & life for 6304
Recommended fits & mounting
- Rotating inner ring on a 20 mm shaft: k5; housing bore H7 for normal stationary-load outer rings. Reverse the logic if the outer ring rotates.
- Fit by induction heating (max 120 °C) where practical — never drive the ring home through the rolling elements.
- Keep shaft and housing fillet radii below the bearing chamfer so the 15 mm-wide ring seats square on its shoulder.
Lubrication strategy
Open execution: the application supplies lubrication. Use the grease relubrication chart for this bearing — pitch diameter dm = 36 mm, so the speed factor at the 19,000 r/min limiting speed is 684,000 mm·r/min. Intervals shorten steeply as that factor rises.
Worked L10 life example (illustrative duty)
For ball bearings, L10h = (C/P)3 · 106 / (60·n). Taking an example radial equivalent load P = 3 kN at n = 1,500 r/min (a small belted motor duty — substitute the real equivalent load from the application calculation):
C = 16.8 kN → L10h ≈ 1,951 hours — a warning that this section is lightly rated for a 3 kN load; a heavier section at the same 20 mm bore is the usual fix
Choosing a section at the same 20 mm bore
| Series | Open execution | OD × width | C (kN) | Limiting speed (r/min) |
|---|---|---|---|---|
| 60xx | 6004-FAG | 42 × 12 | 10.6 | 27,500 |
| 62xx | 6204-FAG | 47 × 14 | 14.7 | 24,300 |
| 63xx | 6304-FAG | 52 × 15 | 16.9 | 19,800 |
| 64xx | 6404-FAG | 72 × 19 | 30.5 | 14,000 |
| 618xx | 61804-FAG | 32 × 7 | 4.0 | 33,500 |
| 619xx | 61904-FAG | 37 × 9 | 6.4 | 28,500 |
| 160xx | 16004 | 42 × 8 | 7.9 | 26,000 |
A larger section is not a drop-in swap — OD and width change — and same-envelope seal variants are compared on the 20×52×15 envelope page. Match meaning, not the size chart alone: see what the cross-reference levels mean.
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 6304-2RS-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6304-FAG | FAG | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 6304-ZZ-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 6304 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the supplier. |
| 6304-2RS-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6304-NSK | NSK | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 6304-RSR-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 6304-ZZ-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 6304-2RS-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6304-NTN | NTN | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
| 6304-RSR-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 6304-ZZ-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 7304 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| NU304 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| W6304-2RS | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF stainless execution W 6304-2RS1 shares the 20×52×15 mm envelope but rates differently (16.8/7.8 kN vs 13.8/7.8 kN) — not a load-rating equivalent. |
| W6304-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF stainless execution W 6304-2Z shares the 20×52×15 mm envelope but rates differently (16.8/7.8 kN vs 13.8/7.8 kN) — not a load-rating equivalent. |
| W6304 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF stainless execution W 6304 shares the 20×52×15 mm envelope but rates differently (16.8/7.8 kN vs 13.8/7.8 kN) — not a load-rating equivalent. |
Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.
How the 6304 model number is decoded
6304 is supplied open, without shields or seals, so the arrangement around it must supply and retain the lubricant. Within the medium 63xx section (diameter series 3 of ISO 15), multiplying bore code 04 by five gives the 20 mm bore; the 52 mm outside diameter and 15 mm width follow the same boundary-dimension plan. For a rotating inner ring on a 20 mm shaft under normal load, catalogue practice seats it on a k5 shaft fit with an H7 housing bore — confirm against the actual load direction and magnitude before committing. In the SKF catalogue this open execution carries the bare designation; protected variants are ordered separately as -2Z and -2RSH.
Typical equipment & failure modes
Common applications
- agricultural equipment
- fans and blowers
- electric motors
- centrifugal pumps
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- raceway smearing under marginal lubrication at start-up
- edge loading from shaft deflection or housing misalignment
Selection pitfalls — read before you substitute
- Sizes around 20 mm bore are normally pressed on cold with a sleeve against the inner-ring face; the press force must never route through the outer ring or the balls of 6304.
- The 63xx medium section at 20 mm bore gains dynamic rating through larger rolling elements on a 52 mm OD; the penalty is mass and a lower limiting speed than the 6204 — do not specify it for speed-critical shafts.
- Storage matters for open bearings: 6304 leaves the factory with rust preventive only, so clean it and apply the service grease at assembly even if the rings look oily from the wrapper.
- Open bearings tolerate the highest speeds in the 6300-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 6304 units.
- Shaft and housing fillets must clear the bearing chamfer so the 15 mm-wide ring seats square; provide an undercut or withdrawal groove instead of relying on an oversized radius.
- Deep-groove ball bearings tolerate only minutes of misalignment; if the 52 mm housing cannot be aligned, switch to a self-aligning type rather than shimming 6304.
- The open 6304 needs external sealing and application-supplied lubrication; in the SKF catalogue the protected variants are separate order numbers 6304-2Z (shields) and 6304-2RSH (contact seals), not suffix-free 6304.
- The 16.8/7.8 kN ratings here are SKF Explorer-class figures from catalogue PUB BU/P1 17000/1 EN (Oct 2018); SKF can revise internal geometry and ratings without changing the designation, so treat the catalogue version and date as part of the specification and re-verify for critical drives.
Frequently asked questions
What are the dimensions of a 6304 bearing?
A 6304 deep-groove ball bearing has a 20 mm bore, 52 mm outer diameter and 15 mm width (0.787 × 2.047 × 0.591 in), per ISO 15 boundary dimensions. It is an open bearing with no seals or shields.
How does the 6304 bore code work?
The last two digits of 6304 are bore code 04, giving 04 × 5 = 20 mm bore. The 52 mm outside diameter and 15 mm width follow the ISO 15 diameter series, not the bore code alone.
What does no suffix on 6304 mean?
A bare 6304 designation means open: no shields or seals, normal CN radial clearance and P0 normal tolerance unless further suffixes are ordered. The application must supply and retain the lubrication.
How does the 6300 compare with other series at the same 20 mm bore?
The '3' is the medium diameter series: 52×15 mm, 16.0 mm radial section at 20 mm bore, carrying more load than a 6204 but needing a larger housing bore and giving up some speed.
What is the SKF designation and catalogue data for 6304?
In the SKF Rolling Bearings catalogue this size is listed as 6304 — the open (unsealed) execution, 20×52×15 mm per ISO 15. Quoted values: C 16.8 kN, C0 7.8 kN, Pu 0.335 kN, limiting speed 19000 r/min, mass 140 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6304.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-25. Read our editorial & correction policy.