6308 bearing: complete specifications & equivalents
The 6308 is a ISO 15 radial bearing sized 40 x 90 x 23 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Bore diameter d | 40 mm |
| Outer diameter D | 90 mm |
| Width B | 23 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 42.3 kN |
| Basic static load rating C0 | 24 kN |
| Fatigue load limit Pu | 1.02 kN |
| Reference speed (thermal) | 17000 rpm |
| Limiting speed (mechanical) | 11000 rpm |
| Operating temperature | -40 to +150 °C |
| Mass | 630 g |
| Manufacturer designation | SKF 6308 |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018) |
| Last verified | 2026-09-24 |
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 | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 0.906 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 25 mm |
| Smallest bore in 6300-series | 10 mm |
| Largest outer diameter in 6300-series | 400 mm |
| Width range across 6300-series | 11–78 mm |
| Bore position in 6300-series (smallest first) | 9 of 30 |
| Bore above smallest 6300-series size | 30 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 6308 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; brand-specific OEM equivalents (NSK/FAG/NTN) pending multi-source data. |
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 6308 model number is decoded
In the 6300-series (ISO 15 diameter series 3) the last two digits encode the bore: 6308 carries bore code 08 = 40 mm. Outside diameter 90 mm and width 23 mm come from the ISO 15 boundary-dimensions general plan. With no seal suffix the bearing is open: no shields or seals are fitted and lubrication is supplied by the application. For normal-load mounting with a rotating inner ring on a 40 mm shaft, typical catalogue practice is a k5 shaft seat with an H7 housing bore — verify against the actual load direction and magnitude. In the SKF catalogue this open execution carries the bare designation; protected variants are ordered separately as -2Z and -2RSH.
Typical equipment & failure modes
Common applications
- electric motors
- centrifugal pumps
- small gearboxes
- conveyors and drives
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- false brinelling from vibration while the shaft is stationary
- fretting corrosion on a loose shaft seat
Selection pitfalls — read before you substitute
- At a 40 mm bore, a shaft-seat burr or an overtight setscrew can score the thin inner ring of 6308; check shaft finish and runout (target Ra ≤ 1.6 µm) before pressing it home.
- The 63xx medium series gains rating at 40 mm bore through a 90 mm OD and 23 mm width; the heavier rolling elements also trade away some speed versus a 6208.
- The open 6308 has no lubricant retention: grease escapes and contaminants migrate straight into the 40×90×23 mm raceway, so specify a sealed arrangement for dusty or washdown duty.
- Open bearings tolerate the highest speeds in the 6300-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 6308 units.
- Suffixes stack in a defined order — clearance follows the seal code, e.g. 6308-C3. No clearance suffix means normal CN clearance.
- The open 6308 needs external sealing and application-supplied lubrication; in the SKF catalogue the protected variants are separate order numbers 6308-2Z (shields) and 6308-2RSH (contact seals), not suffix-free 6308.
- The 42.3/24 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 6308 bearing?
A 6308 deep-groove ball bearing has a 40 mm bore, 90 mm outer diameter and 23 mm width (1.575 × 3.543 × 0.906 in), per ISO 15 boundary dimensions. It is an open bearing with no seals or shields. Geometry-based estimated mass is about 599 g for a steel-cage unit; catalogue masses vary slightly with seal and cage design.
How does the 6308 bore code work?
The last two digits of 6308 are bore code 08, giving 08 × 5 = 40 mm bore. The 90 mm outside diameter and 23 mm width follow the ISO 15 diameter series, not the bore code alone.
What does no suffix on 6308 mean?
A bare 6308 designation means open: no shields or seals, normal CN radial clearance and P0 normal tolerance unless further suffixes are ordered. The application must supply and retain the lubrication.
How does the 6300 compare with other series at the same 40 mm bore?
The '3' is the medium diameter series: 90×23 mm, 25.0 mm radial section at 40 mm bore, carrying more load than a 6208 but needing a larger housing bore and giving up some speed.
What is the SKF designation and catalogue data for 6308?
In the SKF Rolling Bearings catalogue this size is listed as 6308 — the open (unsealed) execution, 40×90×23 mm per ISO 15. Quoted values: C 42.3 kN, C0 24 kN, Pu 1.02 kN, limiting speed 11000 r/min, mass 630 g. Brand suffixes (2Z, 2RSH) differ from the industry-neutral spelling 6308.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018) on 2026-09-24. Read our editorial & correction policy.