31308-DF bearing: complete specifications & equivalents
The 31308-DF is a ISO 355 radial bearing sized 40 x 90 x 50.5 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 | 50.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 156 kN |
| Basic static load rating C0 | 163 kN |
| Fatigue load limit Pu | 19 kN |
| Reference speed (thermal) | 4500 rpm |
| Limiting speed (mechanical) | 7500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1500 g |
| Manufacturer designation | SKF 31308/DF |
| Standard | ISO 355 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.3-8.8 TRB variants |
| Last verified | 2026-09-29 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.3-8.8 TRB variants) · extracted 2026-09-29
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.3-8.8 TRB variants); 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 & matched-df-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 1.988 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 25 mm |
| Smallest bore in matched-df-series | 25 mm |
| Largest outer diameter in matched-df-series | 540 mm |
| Width range across matched-df-series | 34.5–280 mm |
| Bore position in matched-df-series (smallest first) | 4 of 35 |
| Bore above smallest matched-df-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31308 | 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 31308-DF model number is decoded
Clamp the assembled pair axially through the cones — never through the rollers — and verify the 50.5 mm overall width against the catalogue value before final torquing of the shaft nut.Ordering number SKF 31308/DF in SKF catalogue PUB BU/P1 17000 denotes two single-row tapered roller bearings supplied as a matched face-to-face (X) matched pair set for a 40 mm shaft — one order number, one factory setting.Digit by digit, 31308-DF reads as the ISO 355 base bearing 31308 supplied as a face-to-face (X) matched pair matched pair (/DF); the 40 mm bore and 90 mm OD are per-bearing, the 50.5 mm width is for the set. Face-to-face matching puts the small rib ends outward, so the pressure cones cross inside the pair; 31308-DF therefore runs cooler where the shaft expands axially, at the price of lower moment stiffness than an O-arrangement of the same 40 mm bore. Selection arithmetic: the catalogue C 156 kN and C0 163 kN are ratings of the complete pair, not of one bearing — never halve them back to a single-row figure when checking L10 life, and use the pair Pu 19 kN as the fatigue floor. Dimensional interchange map: within its boundary plan the 40×90×50.5 mm envelope of 31308-DF is fixed, so shoulder, spacer and seal drawings can be dimensioned straight from the catalogue table. Setting note for 31308-DF: the axial clearance is set at the factory by selective spacer grinding for the /DF execution; in service, re-checking end play after the first thermal cycle catches seating relaxation before it becomes roller skid.
Typical equipment & failure modes
Common applications
- belt-driven fan and blower shafts
- axle-boxes in material-handling equipment
- automotive and light-truck wheel hubs
- pump and compressor shafts
Known failure patterns
- thermal preload runaway in an O-arrangement pair when inner-ring heat expands the setting
- 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
- rib-roller contact scoring from loss of the EP additive film
- hard-particle indentation of the tapered raceway in unfiltered oil
Selection pitfalls — read before you substitute
- A matched /DF set is ground as one system: never separate the two bearings of 31308-DF or swap the spacer — the factory clearance is lost the moment the set is broken.
- Setting is built into 31308-DF; the classic field error is re-adjusting a matched pair as if it were two loose single bearings, which destroys the /DF clearance class.
- O and X arrangements are not interchangeable by turning the set around: 31308-DF in face-to-face (X) matched pair arrangement has its load-line geometry fixed — specify the arrangement from the shaft thermal and stiffness analysis.
- The 156/163 kN ratings are SKF catalogue 17000 values for this 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.
- Quote the full SKF 31308/DF designation when purchasing — base-number-only orders are ambiguous across executions and variants.
Frequently asked questions
What are the dimensions and catalogue data of 31308-DF?
The SKF 31308/DF is a matched pair of single-row tapered roller bearings in face-to-face (X) matched pair arrangement with 40 mm bore, 90 mm outer diameter and 50.5 mm overall width (1.575 × 3.543 × 1.988 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 156 kN, C0 163 kN, fatigue load limit Pu 19 kN, reference speed 4,500 r/min, limiting speed 7,500 r/min, mass about 1.50 kg.
What does the /DF suffix on 31308-DF mean?
The base 31308 is the ISO 355 single-row bearing; the /DF suffix marks the matched-set execution — the arrangement (face-to-face (X)), the ground spacer and the factory-set axial clearance class. A matched set cannot be assembled from loose single bearings; quote the full designation when ordering.
Are the C and C0 ratings of 31308-DF for one bearing or the pair?
They are for the complete matched pair: C 156 kN dynamic and C0 163 kN static already include load sharing between the two bearings. Do not halve them for single-bearing checks, and do not compare them directly with the single-row 31308 table values.
Can 31308-DF be adjusted like two loose tapered bearings?
No — the axial clearance is set at the factory by selective spacer grinding. Mounting work is limited to clean seats, correct fits (k5 on a rotating 40 mm shaft) and axial clamping through the cones; re-setting in the field destroys the matched clearance class.
When should a face-to-face (X) matched set be chosen?
Choose the face-to-face (X) set where the shaft grows thermally or alignment is imperfect — the converging load lines tolerate deflection. It is the default choice for wheel hubs and general gearbox shafts at the 40 mm bore.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.3-8.8 TRB variants on 2026-09-29. Read our editorial & correction policy.