638-RSR bearing: complete specifications & equivalents
The 638-RSR is a ISO 15 radial bearing sized 8 x 28 x 9 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 | 8 mm |
| Outer diameter D | 28 mm |
| Width B | 9 mm |
| Material | GCr15 |
| Seal / shield | RSR |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 1.33 kN |
| Basic static load rating C0 | 0.57 kN |
| Fatigue load limit Pu | 0.024 kN |
| Reference speed (thermal) | 60000 rpm |
| Limiting speed (mechanical) | 30000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 30 g |
| Manufacturer designation | 638-2RZ |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-27
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 & 63800-series range
| Bore d | 0.315 in |
|---|---|
| Outer diameter D | 1.102 in |
| Width B | 0.354 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 10 mm |
| Smallest bore in 63800-series | 1.5 mm |
| Largest outer diameter in 63800-series | 28 mm |
| Width range across 63800-series | 2–9 mm |
| Bore position in 63800-series (smallest first) | 7 of 8 |
| Bore above smallest 63800-series size | 6.5 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 638-RSR model number is decoded
In the 63800-series, the final digit is the bore in millimetres: 638 fits a 8 mm shaft (direct-number miniature spelling). The envelope is 8×28×9 mm (0.315×1.102×0.354 in) with a 10.0 mm radial section height, C 1.33 kN, C0 0.57 kN and Pu 0.024 kN. SKF lists this as 638-2RZ with a low-friction non-contact seal (2RSL/2RZ spelling): it runs near open-bearing speed with less drag than a contact seal but is not liquid-tight. Limiting speed 30000 r/min, catalogue mass 30 g. A thin section saves space but leaves little margin for misalignment or shaft deflection.
Typical equipment & failure modes
Common applications
- small fans and blowers
- hand-held power tools
- domestic appliances
- instrument and encoder drives
Known failure patterns
- fine dust or moisture passing the low-friction non-contact lip in dirty or wet duty
- grease loss past the low-drag seal when no regreasing schedule is kept
- raceway smearing under marginal lubrication at start-up
- electrical pitting in VFD-driven motors without shaft grounding
Selection pitfalls — read before you substitute
- Deep-groove geometry tolerates only minutes of misalignment; if the 28 mm housing bore cannot be aligned, move to a self-aligning bearing rather than shimming 638-RSR.
- Catalogue ratings for 638-RSR (C 1.33 kN, C0 0.57 kN) are SKF figures from PUB BU/P1 17000; geometry revisions can change ratings without changing the designation, so keep the catalogue edition with the specification.
- The low-friction seal on 638-RSR saves drag versus a contact lip but is not liquid-tight; wet or chemically aggressive positions need the 2RS version.
- Do not pry the caps off 638-RSR to repack it; shield/seal damage leaves a gap that throws grease and admits dirt.
- Do not preload 638-RSR to silence it: a deep-groove ball bearing is not angular-contact, and axial preload only raises temperature and shortens grease life.
- Clearance suffixes follow the seal code in the designation stack (e.g. 638-2Z/C3 in SKF spelling); no suffix means normal CN internal clearance.
Frequently asked questions
What are the dimensions of 638-RSR?
The SKF 638-2RZ measures 8 mm bore × 28 mm OD × 9 mm width (0.315 × 1.102 × 0.354 in), mass about 30 g. It has two low-friction non-contact rubber seals.
How do I read the 638 designation?
Small miniature bearings print the bore as the final digit, so 638 is a 8 mm bearing; the series digits in front give the section (OD/width family).
How heavy is 638-RSR?
Catalogue mass is 30 g for 638-2RZ; seal and cage executions of the same envelope differ by a few grams.
What load can 638-RSR take?
Catalogue values for 638-2RZ: dynamic C 1.33 kN, static C0 0.57 kN, fatigue limit Pu 0.024 kN. Use C in life calculation and C0 for static checks at 8 mm bore.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-27. Read our editorial & correction policy.