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 |
|---|---|
| Brand | SKF |
| 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 | 2026-09-25 |
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 | 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 | 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) | 15 of 40 |
| Bore above smallest 6300-series size | 38 mm |
Mounting, lubrication & life for 6308
Recommended fits & mounting
- Rotating inner ring on a 40 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 23 mm-wide ring seats square on its shoulder.
Lubrication strategy
Open execution: the application supplies lubrication. Use the grease relubrication chart for this bearing — pitch diameter dm = 65 mm, so the speed factor at the 11,000 r/min limiting speed is 715,000 mm·r/min. Intervals shorten steeply as that factor rises.
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 = 42.3 kN → L10h ≈ 31,147 hours
Choosing a section at the same 40 mm bore
| Series | Open execution | OD × width | C (kN) | Limiting speed (r/min) |
|---|---|---|---|---|
| 60xx | 6008-FAG | 68 × 15 | 17.8 | 14,600 |
| 62xx | 6208-FAG | 80 × 18 | 31.5 | 13,600 |
| 63xx | 6308-FAG | 90 × 23 | 47.0 | 11,800 |
| 64xx | 6408-FAG | 110 × 27 | 68.0 | 9,500 |
| 618xx | 61808-FAG | 52 × 7 | 4.9 | 19,300 |
| 619xx | 61908-FAG | 62 × 12 | 14.5 | 15,800 |
| 160xx | 16008 | 68 × 9 | 12.6 | 15,200 |
A larger section is not a drop-in swap — OD and width change — and same-envelope seal variants are compared on the 40×90×23 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 |
|---|---|---|---|
| 6308-2RS-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant (OPEN vs 2RS) and load ratings differ — confirm sealing and rating before substituting. |
| 6308-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 6308-ZZ-FAG | FAG | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant (OPEN vs ZZ) and load ratings differ — confirm sealing and rating before substituting. |
| 6308 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the supplier. |
| 6308-2RS-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6308-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. |
| 6308-RSR-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 6308-ZZ-NSK | NSK | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 6308-2RS-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant differs (OPEN vs 2RS) — confirm sealing suits the duty. |
| 6308-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. |
| 6308-RSR-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant differs (OPEN vs RSR) — confirm sealing suits the duty. |
| 6308-ZZ-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×23 mm envelope per ISO 15; seal variant differs (OPEN vs ZZ) — confirm sealing suits the duty. |
| 7308 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| NU308 | SKF | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | — |
| 1726308-2RS1 | SKF | full Dimensions and internal design equivalent — standard interchange. | SKF 1726308-2RS1 is a standard-inner-ring insert on the same 40x90x23 mm ISO 15 envelope with ratings within 10 %, but its outer surface is sphered for a Y-housing whereas this page is the cylindrical-OD deep-groove bearing — not interchangeable mounts. |
| 308 | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF 308 shares the 40×90×23 mm envelope but catalogue C/C0 differ — envelope match only after a load check. |
| 308-ZZ | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | SKF 308-2Z shares the 40×90×23 mm envelope but catalogue C/C0 differ — envelope match only after a load check. |
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
6308 is supplied open, without shields or seals, so the arrangement around it must supply and retain the lubricant. Within the medium 63xx section (diameter series 3 of ISO 15), multiplying bore code 08 by five gives the 40 mm bore; the 90 mm outside diameter and 23 mm width follow the same boundary-dimension plan. For a rotating inner ring on a 40 mm shaft under normal load, catalogue practice seats it on a k5 shaft fit with an H7 housing bore — confirm against the actual load direction and magnitude before committing. 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.
- The housing bore for the 90 mm OD should be round within IT7; an oval bore pinches the outer ring of 6308 and shows up later as two-point loaded raceway wear.
- Axial location must clamp the ring face, not the seal area: a shoulder or circlip bearing on the seal side of the 23 mm-wide ring of 6308 drags the lip and overheats it.
- 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.
How should 6308 be mounted?
Apply the mounting force to the ring being fitted: on a 40 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 lubrication does 6308 need?
The open 6308 is lubricated by the application; a NLGI 2 lithium-soap grease filled to roughly 25–35% of the free volume is the common choice, with a defined relubrication interval.
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 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, 2RSL) 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 2026-09-25. Read our editorial & correction policy.