6304-RSR bearing: complete specifications & equivalents
The 6304-RSR is a ISO 15 radial bearing sized 20 x 52 x 15 mm (bore x OD x width) with RSR 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 | RSR |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 15.9 kN |
| Basic static load rating C0 | 7.8 kN |
| Fatigue load limit Pu | 0.335 kN |
| Reference speed (thermal) | 30000 rpm |
| Limiting speed (mechanical) | 15000 rpm |
| Operating temperature | -30 to +120 °C |
| Mass | 150 g |
| Manufacturer designation | SKF 6304-2RSL |
| 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-RSR
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
Non-contact low-drag seal lips retain the factory grease but are not liquid-tight. Treat as grease-for-life in light, dry duty; in dirty or wet positions plan replacement around contamination rather than fatigue.
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 = 15.9 kN → L10h ≈ 1,654 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 (RSR vs 2RS) — confirm sealing suits the duty. |
| 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 (RSR 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 (RSR 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 | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 20×52×15 mm envelope per ISO 15; seal variant differs (RSR vs 2RS) — confirm sealing suits the duty. |
| 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 (RSR vs OPEN) — confirm sealing suits the duty. |
| 6304-RSR-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-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 (RSR 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 (RSR vs 2RS) — confirm sealing suits the duty. |
| 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 (RSR vs OPEN) — confirm sealing suits the duty. |
| 6304-RSR-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-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 (RSR 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 (15.9/7.8 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 (15.9/7.8 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 (15.9/7.8 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-RSR 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 -RSR denotes two low-friction non-contact elastomer seals; they keep coarse debris out with minimal drag but are not liquid-tight. 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 low-friction seal suffix is 2RSL/2RZ (this page's industry-neutral spelling is -RSR); catalogue number 6304-2RSL.
Typical equipment & failure modes
Common applications
- small gearboxes
- conveyors and drives
- agricultural equipment
- fans and blowers
Known failure patterns
- ingress of fine dust or moisture past the non-contact lip in dirty or wet duty (RSR is not liquid-tight)
- lip-lubricant starvation if the bearing runs dry for extended periods
- false brinelling from vibration while the shaft is stationary
- fretting corrosion on a loose shaft seat
Selection pitfalls — read before you substitute
- A 20 mm shaft for 6304 should be finished to Ra ≤ 1.6 µm with square seating faces; at this bore a scored or oval journal shows up directly as running noise and early raceway damage.
- The 63xx medium series gains rating at 20 mm bore through a 52 mm OD and 15 mm width; the heavier rolling elements also trade away some speed versus a 6204.
- RSR low-friction seals on 6304-RSR run faster than contact-seal 6304-2RS but let fine dust and moisture past the non-contact lip; in dirty or wet duty specify 6304-2RS instead.
- The non-contact lip of 6304-RSR does not retain a lifetime grease fill the way a contact seal does; confirm the regreasing interval for the 20 mm bore position before relying on it as sealed-for-life.
- Axial location must clamp the ring face, not the seal area: a shoulder or circlip bearing on the seal side of the 15 mm-wide ring of 6304-RSR drags the lip and overheats it.
- A 20 mm bore listing showing the right d/D/B but no standard or precision-class reference may be a loose-tolerance import; measure bore/OD spread before fitting it to a machined shaft.
- SKF catalogues the low-friction seal as 6304-2RSL (suffix -2RSL or -2RZ): a non-contact elastomer lip that runs near the open 15000 r/min limiting speed, closer to the open bearing's 30000 r/min reference than the contact-seal version. It keeps coarse debris out without the drag of a contact seal, but is not liquid-tight — use 2RSH for wet or fine-dust positions.
- The 15.9/7.8 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-RSR bearing?
A 6304-RSR 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 low-friction non-contact rubber seals.
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 internal clearance does 6304-RSR have?
Unless a clearance suffix says otherwise, 6304-RSR is manufactured to normal (CN) radial internal clearance. Tight fits and hot shafts consume clearance in service — for those conditions order the C3 execution of 6304 and verify the residual clearance after mounting.
How should 6304-RSR be mounted?
Apply the mounting force to the ring being fitted: on a 20 mm shaft seat the press load must pass through the inner-ring face only. A fitting sleeve and an arbor press are normally sufficient at this size. Never strike the outer ring, the cage or the seals.
What is the SKF designation and catalogue data for 6304-RSR?
In the SKF Rolling Bearings catalogue this size is listed as 6304-2RSL — two low-friction non-contact elastomer seals, 20×52×15 mm per ISO 15. Quoted values: C 15.9 kN, C0 7.8 kN, Pu 0.335 kN, limiting speed 15000 r/min, mass 150 g. Brand suffixes (2Z, 2RSH, 2RSL) differ from the industry-neutral spelling 6304-RSR.
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.