6304-2RS bearing: complete specifications & equivalents
The 6304-2RS is a ISO 15 radial bearing sized 20 x 52 x 15 mm (bore x OD x width) with 2RS sealing. 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 | 2RS |
| 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 |
| Limiting speed (mechanical) | 9500 rpm |
| Operating temperature | -30 to +110 °C |
| Mass | 150 g |
| Manufacturer designation | SKF 6304-2RSH |
| 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 6304-2RS
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
Contact-sealed execution: greased and sealed for life, no relubrication path. Grease life — not steel fatigue — usually sets the replacement interval; rising running temperature or noise near the end of service is the practical trigger.
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 | 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-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (2RS vs OPEN) — confirm sealing suits the duty. |
| 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 (2RS vs ZZ) — confirm sealing suits the duty. |
| 6304 | ISO 15 | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | ISO 15 boundary-dimension envelope; seal suffix convention varies by brand (2RS / DDU / LLU / 2RSR) — verify seal design and temperature range before substituting. |
| 6304-2RS-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-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (2RS vs OPEN) — confirm sealing suits the duty. |
| 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 (2RS 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 (2RS vs ZZ) — confirm sealing suits the duty. |
| 6304-2RS-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-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (2RS vs OPEN) — confirm sealing suits the duty. |
| 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 (2RS 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 (2RS 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 6304-2RS model number is decoded
In the 6300-series (diameter series 3 of ISO 15) the last two digits encode the bore: 6304 carries bore code 04 = 20 mm. Outside diameter 52 mm and width 15 mm come from the ISO 15 boundary-dimensions general plan. Suffix -2RS denotes two contact-type elastomer seals over a lifetime grease fill; the sealing lips add drag compared with open or shielded versions. For normal-load mounting with a rotating inner ring on a 20 mm shaft, typical catalogue practice is a k5 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. SKF's contact-seal catalogue number is 6304-2RSH (older text: -2RS1), mapped here from the industry-neutral -2RS spelling.
Typical equipment & failure modes
Common applications
- agricultural equipment
- fans and blowers
- electric motors
- centrifugal pumps
Known failure patterns
- seal-lip hardening and loss of pre-grease in sustained high-temperature service
- grease-life expiry in the sealed-for-life cavity (no relubrication path)
- electrical pitting in VFD-driven motors without grounding protection
- raceway smearing under marginal lubrication at start-up
Selection pitfalls — read before you substitute
- At a 20 mm bore, a shaft-seat burr or an overtight setscrew can score the thin inner ring of 6304-2RS; check shaft finish and runout (target Ra ≤ 1.6 µm) before pressing it home.
- 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.
- Heat is the enemy of the sealed 6304-2RS: sustained running near the lip temperature limit hardens the rubber, after which grease escapes and dirt tracks in — watch the housing temperature in hot drives.
- Never wash a sealed 6304-2RS in solvent or press it home via the outer ring; solvent destroys the grease thickener and mounting force through the seal deforms the lip.
- Vibration during standstill brinells the raceways of a 20 mm bearing at ball spacing; if the machine sits idle next to running equipment, turn the shaft over periodically or isolate the arrangement.
- Grease compatibility is not guaranteed between fills: mixing lithium and polyurea thickeners in a 6300-series position can soften the mixture and leak — clean out the old fill before switching grease types.
- SKF catalogues the contact-sealed version as 6304-2RSH (older printings may read -2RS1); it is shipped pre-greased and its 9500 r/min limiting speed is set by seal-lip drag and grease life versus the open bearing's 30000 r/min thermal reference speed. The single-seal catalogue number is 6304-RSH, used where one shaft side needs external relubrication.
- A one-seal execution 6304-RSH exists for arrangements that lubricate through the open side; fitting 6304-2RSH instead means lifetime grease and no external oil supply — mixing the two in the same shaft can starve the sealed position.
- 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 6304-2RS bearing?
A 6304-2RS 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 fitted with two contact rubber seals and is normally pre-greased.
What does the 2RS suffix on 6304-2RS mean?
2RS means two contact elastomer seals, one each side, usually over a lifetime grease fill. Sealing against dust and moisture is better than ZZ shields, but the lip drag lowers the speed and temperature ceiling.
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.
Are 6304 bearings from different brands interchangeable?
For boundary dimensions, yes: every brand's 6304 uses the same ISO 15 envelope (20×52×15 mm). Load ratings, limiting speeds, clearance, precision class and sealing design can differ, so verify those in the supplier catalogue when substituting. Seal suffixes also differ by brand (2RS, DDU, LLU, 2RSL and similar).
What is the SKF designation and catalogue data for 6304-2RS?
In the SKF Rolling Bearings catalogue this size is listed as 6304-2RSH — two contact elastomer seals over a lifetime grease fill, 20×52×15 mm per ISO 15. Quoted values: C 16.8 kN, C0 7.8 kN, Pu 0.335 kN, limiting speed 9500 r/min, mass 150 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6304-2RS.
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.