RNA6904 bearing: complete specifications & equivalents
The RNA6904 is a ISO 1206 radial bearing sized 25 x 37 x 30 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 25 mm |
| Outer diameter D | 37 mm |
| Width B | 30 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 35.2 kN |
| Basic static load rating C0 | 53 kN |
| Fatigue load limit Pu | 6.55 kN |
| Reference speed (thermal) | 15000 rpm |
| Limiting speed (mechanical) | 17000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 100 g |
| Manufacturer designation | RNA 6904 |
| Standard | ISO 1206 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without an inner ring |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without an inner ring) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without an inner ring); 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 & RNA-69-series range
| Bore d | 0.984 in |
|---|---|
| Outer diameter D | 1.457 in |
| Width B | 1.181 in |
| ISO bore code | 04 |
| Radial section height (D−d)/2 | 6 mm |
| Smallest bore in RNA-69-series | 16 mm |
| Largest outer diameter in RNA-69-series | 130 mm |
| Width range across RNA-69-series | 22–63 mm |
| Bore position in RNA-69-series (smallest first) | 4 of 22 |
| Bore above smallest RNA-69-series size | 9 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NX25-Z | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (35.2/53 vs 15.1/24.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NX25 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (35.2/53 vs 15.1/24.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NKX25-Z | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (35.2/53 vs 19/32.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NKX25 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (35.2/53 vs 19/32.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NKXR25 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (35.2/53 vs 19/32.5 kN) — boundary dimensions match, not a load-rating equivalent. |
| NKXR25-Z | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 25×37×30 mm envelope, but catalogue C/C0 differ between the executions (35.2/53 vs 19/32.5 kN) — boundary dimensions match, 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 RNA6904 model number is decoded
In SKF catalogue PUB BU/P1 17000, RNA 6904 designates a flanged, machined outer ring filled with needle rollers and a cage for a 25 mm shaft — heavier section and higher accuracy than a drawn cup, with no inner ring so the journal is the raceway. In SKF nomenclature RNA families drop the inner ring: the numbers after the letters give the 25 mm under-roller diameter and the 30 mm width, with the 37 mm outside diameter set by the dimension series 69 needle roller bearings without inner ring plan. SKF offers this family open as standard; a matching IR inner ring can be added separately when the shaft cannot be hardened, which converts the envelope into the NKI/NA equivalent. For life calculation, the 35.2/53 kN ratings assume raceway geometry supplied by the shaft and housing in families without an inner ring — journal hardness, roundness and finish are part of the bearing, not of the application. Mounting: the flanged outer ring presses into the H7 housing bore against its flange face; the shaft (hardened to 58–64 HRC, ground) enters afterwards, and axial retention is by the housing wall plus a cover washer.
Typical equipment & failure modes
Common applications
- guide rollers running on hardened tracks
- swing arms and lever pivots with oscillating duty
- cam followers built up from separate components
- crank pins and eccentrics where the hardened journal is the raceway
Known failure patterns
- needle edge loading and raceway denting when the shaft deflects beyond the compensation range
- cage pocket wear and roller skew after sustained operation with too little radial preload
- grease starvation at the roller ends when relubrication intervals are stretched in dirty duty
- rolling-contact fatigue spalling after the rated L10 life
- rapid raceway scoring when the shaft journal hardness drops below 58 HRC or the ground finish wears away
Selection pitfalls — read before you substitute
- On a 25 mm seat the housing bore quality dominates life: a bore 0.02 mm out of round pinches the 37 mm ring or cup into a lobed shape, and the rollers then trace the housing's geometry error, not the design load.
- Reference and limiting speeds are different limits: the 15,000 r/min reference is the thermal criterion under load, The limiting value is mechanical; the reference value is thermal under load, and grease choice moves it substantially.
- Hardness is load capacity: in families without an inner ring the 25 mm journal must hold 58–64 HRC with a ground finish; a surface that looks fine but sits at 45 HRC will rib the raceway within weeks.
- The 35.2/53 kN ratings and 100 g mass are SKF catalogue values transcribed from ch. 7.3 of PUB BU/P1 17000 (PDF table page 628); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
Is the RNA 6904 sealed?
No — this execution is open and depends on the housing sealing arrangement; grease it at assembly and keep the relubrication interval short in dirty duty.
Which dimensions does the RNA 6904 have?
A RNA 6904 measures 25 mm bore/Fw × 37 mm outside diameter × 30 mm width (0.984 × 1.457 × 1.181 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 35.2 kN, static C0 53 kN, fatigue limit Pu 6.55 kN, limiting speed 17,000 r/min, reference speed 15,000 r/min, mass about 100 g.
What does RNA 6904 mean in SKF part numbering?
RNA names a machined-ring needle roller bearing without inner ring: the figures give Fw 25 mm and width 30 mm, OD 37 mm comes from the dimension series, and the flanged outer ring retains the caged rollers.
Does the RNA 6904 need a hardened and ground shaft?
No. In this execution the 25 mm shaft journal is the inner raceway: it must be ground and hardened to 58–64 HRC (with matching housing bore quality on the outside). If the shaft cannot meet that, order the inner-ring sibling (NKI/NA execution) plus its ground inner ring instead.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.3 machined rings with flanges, without an inner ring on 2026-09-26. Read our editorial & correction policy.