NA4904-2RS bearing: complete specifications & equivalents
The NA4904-2RS is a ISO 1206 radial bearing sized 20 x 37 x 18 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 | 37 mm |
| Width B | 18 mm |
| Material | GCr15 |
| Seal / shield | 2RS |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | none |
| Basic dynamic load rating C | 19.4 kN |
| Basic static load rating C0 | 22.4 kN |
| Fatigue load limit Pu | 2.65 kN |
| Limiting speed (mechanical) | 7500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 80 g |
| Manufacturer designation | NA 4904.2RS |
| Standard | ISO 1206 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with 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. 7.4 machined rings with flanges, with 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 & NA-49-series range
| Bore d | 0.787 in |
|---|---|
| Outer diameter D | 1.457 in |
| Width B | 0.709 in |
| ISO bore code | 04 |
| Radial section height (D−d)/2 | 8.5 mm |
| Smallest bore in NA-49-series | 10 mm |
| Largest outer diameter in NA-49-series | 190 mm |
| Width range across NA-49-series | 13–50 mm |
| Bore position in NA-49-series (smallest first) | 5 of 28 |
| Bore above smallest NA-49-series size | 10 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the NA4904-2RS model number is decoded
NA 4904.2RS provides the full machined-ring needle roller construction: ground inner ring on a 20 mm seat, flanged outer ring at 37 mm, caged needles between them — the standard choice when a replaceable inner raceway is required. Reading the designation: the letters name the series with inner ring, the numbers the boundary plan — 20 mm bore (d), 18 mm width; the 37 mm OD follows the dimension series, and the inner ring is a separate ground component. TN polymer cage executions run quieter and tolerate grease-lubricated pivot duty; steel cage executions remain the choice for higher temperature or oil-bath lubrication. Catalogue mass 80 g at 20×37×18 mm makes this one of the highest capacity-per-gram choices in the dimension series 49 needle roller bearings with inner ring; the limit is usually the shaft's ability to serve as a raceway, not the rolling contact itself. For NA 49 2RS executions the wider outer ring changes the housing depth: verify the 18 mm width and s offset dimensions against the open execution before reusing an existing bore.
Typical equipment & failure modes
Common applications
- printing and paper-handling rollers
- gearbox shafts where the journal cannot be hardened on site
- wheel and lever pivots needing a replaceable inner ring
- conveyor roller ends and return rollers
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
- abrasive paste formation from dust ingressing past open ends without effective housing seals
- electrical erosion on VFD-driven shafts without brush or insulated mounting
- inner-ring raceway spalling after the narrow ring section runs hot with excessive interference
Selection pitfalls — read before you substitute
- On a 20 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.
- The quoted 19.4/22.4 kN ratings are SKF catalogue values for this exact execution (NA 4904.2RS); ratings can be revised without the order number changing, so keep the catalogue version (SKF catalogue PUB BU/P1 17000) with the drawing.
- Oscillating pivots fail differently: rocking through a small angle concentrates wear in the same roller positions — inspect those zones, and consider rotating the assembly's clock position at service intervals.
- The 19.4/22.4 kN ratings and 80 g mass are SKF catalogue values transcribed from ch. 7.4 of PUB BU/P1 17000 (PDF table page 640); combined-type axial ratings appear in the text above because the structured record carries radial values only.
Frequently asked questions
What mounting mistakes ruin a NA 4904.2RS?
Mount the inner ring on the 20 mm seat first (induction heat, max 120 °C, or press), then fit the flanged outer ring into the H7 housing bore. Verify free rotation and, for 2RS executions, check the wider outer ring against the housing depth.
Is the NA 4904.2RS sealed?
Yes — the 2RS execution seals both faces with rubber contact seals; note its wider outer ring (B and s differ from the open execution), so housing dimensions must be re-checked.
Which dimensions does the NA 4904.2RS have?
A NA 4904.2RS measures 20 mm bore/Fw × 37 mm outside diameter × 18 mm width (0.787 × 1.457 × 0.709 in). From SKF catalogue PUB BU/P1 17000: radial dynamic rating C 19.4 kN, static C0 22.4 kN, fatigue limit Pu 2.65 kN, limiting speed 7,500 r/min, mass about 80 g.
What does NA 4904.2RS mean in SKF part numbering?
The letters mark a machined-ring needle roller bearing with inner ring: 20 mm bore, 18 mm width, 37 mm OD per the series plan. The hardened inner ring is the raceway, so an ordinary k5 shaft seat suffices.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 7.4 machined rings with flanges, with an inner ring on 2026-09-26. Read our editorial & correction policy.