30308 bearing: complete specifications & equivalents
The 30308 is a ISO 355 radial bearing sized 40 x 90 x 25.25 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 | 25.25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 106 kN |
| Basic static load rating C0 | 95 kN |
| Fatigue load limit Pu | 10.8 kN |
| Reference speed (thermal) | 6300 rpm |
| Limiting speed (mechanical) | 8000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 730 g |
| Manufacturer designation | SKF 30308 |
| Standard | ISO 355 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB); 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 & 30300-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 0.994 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 25 mm |
| Smallest bore in 30300-series | 15 mm |
| Largest outer diameter in 30300-series | 500 mm |
| Width range across 30300-series | 14.25–105 mm |
| Bore position in 30300-series (smallest first) | 7 of 32 |
| Bore above smallest 30300-series size | 25 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30308 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 355 boundary-dimension envelope; brand-specific OEM equivalents (NSK/FAG/NTN) pending multi-source data. |
| 30308-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. |
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 30308 model number is decoded
SKF 30308 belongs to the SKF single-row tapered roller range — the 40 mm bore entry in the 30300 series, dimensioned 90 mm OD and 25.25 mm wide to the ISO 355 boundary plan.Digit by digit, 30308 reads as bearing type 3 (single-row tapered roller), heavy-OD section series 03, and bore reference 08 resolving to 40 mm; 90 mm OD and 25.25 mm width are the matching ISO 355 boundary values. The SKF catalogue adds the ISO 355 dimension-series code after the bare number (e.g. 2FB); it is the dimensional series, not a separate part number. The 10.8 kN Pu figure feeds the adjusted-life equation at contaminated or partial-film conditions, and the 0.90 C0/C balance shows this execution is tuned to thrust-heavy combined loads rather than pure radial running. Fit selection follows the rotating ring — interference on a rotating cone — and two 30308 units are required to take reversing thrust; keep the induced axial load inside the rated capacity when calculating the pair.
Typical equipment & failure modes
Common applications
- belt-driven fan and blower shafts
- axle-boxes in material-handling equipment
- automotive and light-truck wheel hubs
- industrial gearbox shafts and reducers
Known failure patterns
- cup or cone misalignment when the separable rings are not seated square during mounting
- loose cup rotation in the housing when the specified press fit is not achieved
- uneven load sharing in a pair when spacer faces are not parallel to the bore
- thermal preload runaway in an O-arrangement pair when inner-ring heat expands the setting
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- electrical pitting on VFD-driven shafts without grounding protection
Selection pitfalls — read before you substitute
- On this 40 mm bore, interference and temperature rise consume clearance inside a preloaded pair; calculate the residual clearance after mounting and at operating temperature — an over-tight 30308 pair heats, loses setting control and smears the roller-rib contact.
- The 303 series at 40 mm bore (90×25.25 mm) carries a larger OD and higher capacity than 30208 at the same bore; the bigger section runs hotter, so re-check the 8,000 r/min speed ceiling and shoulder diameters before substituting.
- The tapered contact angle creates an induced axial load under pure radial force; include it in the 30308 rating calculation (and account for it in both bearings of a pair) or the unloaded bearing skids its rollers.
- A single 30308 cannot locate the shaft axially in both directions; mounting it singly on a reversing-thrust shaft leaves one direction uncontrolled — always use an O or X matched pair for bidirectional location.
- The 730 g mass and 25.25 mm width mean spacer and abutment faces must be square to the axis within the bearing's own P0 tolerance; a tilted spacer tilts the contact angle and concentrates load on one rib of 30308.
- The 106/95 kN ratings are SKF catalogue 17000 values for the basic execution; SKF can revise internal geometry without changing the order number, so keep the catalogue version (PUB BU/P1 17000/1 EN, 2018) with the specification and re-verify for critical drives.
- SKF lists several executions of 30308 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 30308 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What are the dimensions and catalogue data of 30308?
The SKF 30308 is a single-row tapered roller bearing with 40 mm bore, 90 mm outer diameter and 25.25 mm width (1.575 × 3.543 × 0.994 in) per ISO 355. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 106 kN, C0 95 kN, fatigue load limit Pu 10.8 kN, reference speed 6,300 r/min, limiting speed 8,000 r/min, mass about 730 g. It is an open, separable bearing with a pressed-steel cage.
How does the 30308 bore code work?
The last two digits of 30308 are bore code 08, so 08 × 5 = 40 mm bore. The 90 mm OD and 25.25 mm width come from the ISO 355 dimension-series plan, shared with other tapered bearings of the same code.
What do the 30308 series and basic execution designations mean?
The leading 3 marks a single-row tapered roller bearing; the second digit 03 is the ISO 355 series (heavy-OD section). The SKF catalogue lists the ISO 355 dimension-series code after the bare number. A steeper-contact-angle variant (B suffix) is a different order number and is not interchangeable with the basic execution.
Can a single 30308 take axial load in both directions?
No — one single-row tapered roller bearing reacts thrust in one direction only, and under radial load its contact angle induces an axial force. Use two bearings as a matched pair: O (back-to-back) for a rigid, moment-resisting arrangement, X (face-to-face) where thermal expansion must be tolerated, or tandem where one-direction thrust is shared.
How does 30308 compare with a ball bearing of the same bore?
A tapered roller bearing has line contact and a steep contact angle: much higher combined axial-plus-radial capacity and shock resistance than a ball bearing of the same bore, at the cost of speed, one-direction thrust, mandatory pairing for reversing loads and a minimum axial load requirement. A ball bearing cannot be dropped into a combined-load 30308 position and vice versa — verify load direction, Fa/Fr ratio and speed before substituting.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB on 2026-09-26. Read our editorial & correction policy.