31309-DF bearing: complete specifications & equivalents
The 31309-DF is a ISO 355 radial bearing sized 45 x 100 x 54.5 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 45 mm |
| Outer diameter D | 100 mm |
| Width B | 54.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 194 kN |
| Basic static load rating C0 | 204 kN |
| Fatigue load limit Pu | 24.5 kN |
| Reference speed (thermal) | 4000 rpm |
| Limiting speed (mechanical) | 6700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 2000 g |
| Manufacturer designation | SKF 31309/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 | 1.772 in |
|---|---|
| Outer diameter D | 3.937 in |
| Width B | 2.146 in |
| ISO bore code | 09 |
| Radial section height (D−d)/2 | 27.5 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) | 5 of 35 |
| Bore above smallest matched-df-series size | 20 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31309 | 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 31309-DF model number is decoded
SKF 31309/DF belongs to the SKF matched tapered-roller range — the 45 mm bore entry in face-to-face (X) matched pair arrangement, dimensioned 100 mm OD and 54.5 mm overall width for the pair.The code breaks down as base bearing 31309 plus matched-set suffix /DF: two bearings of the 45 mm bore size, paired face-to-face (X) matched pair, with the 54.5 mm overall width spanning the whole arrangement. In the face-to-face (X) arrangement the load lines of the two bearings converge toward the shaft axis: the set tolerates shaft deflection and thermal growth better than a back-to-back pair, but is less stiff against overturning moments. The 54.5 mm overall width of 31309-DF is the axial space the pair occupies. Speed planning for the set uses the catalogue pair values: 4,000 r/min thermal reference and 6,700 r/min mechanical limiting speed — a matched pair runs warmer than one bearing because two roller sets share the 54.5 mm space. Operating context for the 45 mm bore: a shaft of this diameter typically runs in the medium-bore band of industrial duty, and the 100 mm OD places the housing shoulder near 108 mm outer abutment. Mounting order matters for 31309-DF: seat the first bearing, fit the ground spacer, then the second bearing, and clamp axially as a unit — the 54.5 mm catalogue width is the assembled result and the gauge for correct assembly. A matched /DF set needs no setting adjustment at mounting: the clearance is built in; the assembler's job is clean seats, correct fits (k5 on a 45 mm rotating shaft) and square abutments.
Typical equipment & failure modes
Common applications
- axle-boxes in material-handling equipment
- automotive and light-truck wheel hubs
- industrial gearbox shafts and reducers
- axle-boxes in material-handling equipment
Known failure patterns
- preload loss as the mounted pair relaxes, letting rollers skid and smear the raceways
- 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
- electrical pitting on VFD-driven shafts without grounding protection
Selection pitfalls — read before you substitute
- Replace 31309-DF as a complete set: pairing a new bearing with a worn partner leaves the clearance undefined even when the designation matches.
- Clamp the 31309-DF pair axially through the cones, never through the rollers; pressing force across the roller complement brinells the raceways of both bearings at once.
- A matched /DF set is ground as one system: never separate the two bearings of 31309-DF or swap the spacer — the factory clearance is lost the moment the set is broken.
- The 194/204 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 31309/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 31309-DF?
The SKF 31309/DF is a matched pair of single-row tapered roller bearings in face-to-face (X) matched pair arrangement with 45 mm bore, 100 mm outer diameter and 54.5 mm overall width (1.772 × 3.937 × 2.146 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 194 kN, C0 204 kN, fatigue load limit Pu 24.5 kN, reference speed 4,000 r/min, limiting speed 6,700 r/min, mass about 2.00 kg.
What does the /DF suffix on 31309-DF mean?
The base 31309 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 31309-DF for one bearing or the pair?
They are for the complete matched pair: C 194 kN dynamic and C0 204 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 31309 table values.
Can 31309-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 45 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 45 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.