7308 bearing: complete specifications & equivalents
The 7308 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 |
| Seal / shield | open |
| Internal clearance | CN / C3 available |
| Tolerance class | P0 |
| Cage | brass |
| Operating temperature | -40 to +150 °C |
| Mass (geometry estimate) | 599 g |
| Standard | ISO 15 |
| Catalog version | iso15-ed4-geometry |
| Last verified | 2026-09-24 |
Source: ISO 15 boundary-dimensions standard · extracted 2026-09-24
Standard-interchange bearing: dimensions per ISO 15; CN clearance, P0 tolerance and a stamped-steel cage are catalogue defaults unless the supplier states otherwise, and mass is a geometry-derived estimate. Brand catalogue load ratings and limiting speeds for 7308 are being backfilled — use the inquiry form for certified values.
Dimensions in inches & 7300-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 7300-series | 10 mm |
| Largest outer diameter in 7300-series | 240 mm |
| Width range across 7300-series | 11–50 mm |
| Bore position in 7300-series (smallest first) | 9 of 23 |
| Bore above smallest 7300-series size | 30 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7308 | 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 7308 model number is decoded
In the 7300-series (ISO 15 diameter series 3) the last two digits encode the bore: 7308 carries bore code 08 = 40 mm. Outside diameter 90 mm and width 23 mm come from the ISO 15 boundary-dimensions general plan, shared with the 6308 deep-groove envelope. The '7' prefix marks a single-row angular-contact design with an asymmetric raceway and a nominal 40° contact angle (suffix C); a higher-angle variant carries more axial load, a 25° (E / A5) variant runs faster. For combined radial and axial load with a rotating inner ring on a 40 mm shaft, specify a k5 shaft seat with an H7 housing bore — verify against the load direction and magnitude, and pair two units (DB or DF) for bidirectional thrust.
Typical equipment & failure modes
Common applications
- pump and compressor shafts
- small machine tool spindles
- servo and stepper drives
- gear reducers
Known failure patterns
- edge loading and early spalling from shaft deflection or housing misalignment
- electric pitting in VFD-driven spindles without shaft grounding protection
- raceway spalling from axial overload exceeding the single-direction thrust rating
- preload loss after a paired set runs loose, letting the balls skid and smear the raceway
Selection pitfalls — read before you substitute
- At a 40 mm bore, shaft-seat finish and runout (target Ra ≤ 0.8 µm) govern angular-contact noise; a rough or out-of-round seat shows up as spindle runout before it shows as failure.
- The 73xx medium section gains axial and radial rating at 40 mm bore through a 90 mm OD and 23 mm width; the heavier balls also trade away speed versus a 7208 angular contact.
- Angular-contact 7308 tolerates only minutes of misalignment; a deflected shaft or a tilted housing face edge-loads the asymmetric raceway and spalls it early — align the seats to better than 0.001 radian.
- Preload class matters: a 7308 in a DB pair is supplied as preload class light (L) for speed or heavy (H) for rigidity; mixing unmarked bearings in a pair gives uneven preload and short life.
Frequently asked questions
What are the dimensions of a 7308 angular-contact bearing?
A 7308 single-row angular-contact 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 a nominal 40° contact angle. Geometry-based estimated mass is about 599 g for a brass-cage unit; catalogue masses vary with cage and ball complement.
How does the 7308 bore code work?
The last two digits of 7308 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, shared with the 6308 deep-groove envelope.
What is the contact angle of 7308?
The nominal contact angle is 40° (suffix C): a higher angle carries more axial load but limits speed. A 25° (suffix E or A5) variant runs faster and is preferred for high-speed spindles; a 15° (suffix C7) version exists for very-high-speed duty. Confirm the angle and ball complement in the supplier catalogue.
Can a single 7308 take axial load in both directions?
No. A single-row angular-contact bearing carries axial load in one direction only. For bidirectional thrust, mount a matched pair — DB (back-to-back) for a rigid, moment-resisting arrangement with preload class light (L) for speed or heavy (H) for stiffness, DF (face-to-face) for thermal expansion tolerance, or DT (tandem) to share one-direction load.
How does 7308 compare with a deep-groove 6308?
Both share the 40×90×23 mm ISO 15 envelope (25.0 mm radial section), but the angular-contact 7308 has an asymmetric raceway and 40° contact angle: it carries higher combined axial+radial load and runs with controlled preload, but is slower, noisier and needs pairing — it is not a drop-in replacement for a deep-groove 6308.
Reviewed & verified by the MPN Base engineering desk against source catalog iso15-ed4-geometry on 2026-09-24. Read our editorial & correction policy.