31311-DF bearing: complete specifications & equivalents
The 31311-DF is a ISO 355 radial bearing sized 55 x 120 x 63 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 55 mm |
| Outer diameter D | 120 mm |
| Width B | 63 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 256 kN |
| Basic static load rating C0 | 275 kN |
| Fatigue load limit Pu | 33.5 kN |
| Reference speed (thermal) | 3400 rpm |
| Limiting speed (mechanical) | 5600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 3250 g |
| Manufacturer designation | SKF 31311/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 | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 2.48 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 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) | 7 of 35 |
| Bore above smallest matched-df-series size | 30 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31311 | 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 31311-DF model number is decoded
Material and manufacturing detail: the 3250 g catalogue mass reflects through-hardened bearing steel machined to the listed envelope; ring roundness and width tolerance keep the mounted-setting scatter inside the catalogue class. Inspection shorthand: at overhaul, mark both bearings and the spacer of 31311-DF before disassembly — the set is a matched system, and re-assembling with one component reversed changes the factory setting. 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 55 mm rotating shaft) and square abutments.SKF 31311/DF belongs to the SKF matched tapered-roller range — the 55 mm bore entry in face-to-face (X) matched pair arrangement, dimensioned 120 mm OD and 63 mm overall width for the pair.Numbering ties the set to its envelope: base 31311 fixes the 55 mm bore and 120 mm OD of each bearing, the /DF suffix fixes the arrangement and setting, and the catalogue 63 mm width is the combined pair dimension. Face-to-face matching puts the small rib ends outward, so the pressure cones cross inside the pair; 31311-DF therefore runs cooler where the shaft expands axially, at the price of lower moment stiffness than an O-arrangement of the same 55 mm bore. With a pair mass of 3250 g across the 55×120×63 mm envelope, the set replaces what would otherwise be two separate bearings plus spacer grinding work — the factory setting is the engineering value being purchased.
Typical equipment & failure modes
Common applications
- pump and compressor shafts
- machine-tool spindles
- belt-driven fan and blower shafts
- machine-tool spindles
Known failure patterns
- axial overload spalling at the roller-rib contact beyond the single-row thrust rating
- roller large-end smearing against the cone rib after EP lubricant film failure
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- grease degradation after long shelf storage without rotation or re-greasing
- fretting corrosion on a loose rotating shaft seat
Selection pitfalls — read before you substitute
- A matched /DF set is ground as one system: never separate the two bearings of 31311-DF or swap the spacer — the factory clearance is lost the moment the set is broken.
- Clamp the 31311-DF pair axially through the cones, never through the rollers; pressing force across the roller complement brinells the raceways of both bearings at once.
- Replace 31311-DF as a complete set: pairing a new bearing with a worn partner leaves the clearance undefined even when the designation matches.
- The 256/275 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 31311/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 31311-DF?
The SKF 31311/DF is a matched pair of single-row tapered roller bearings in face-to-face (X) matched pair arrangement with 55 mm bore, 120 mm outer diameter and 63 mm overall width (2.165 × 4.724 × 2.48 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 256 kN, C0 275 kN, fatigue load limit Pu 33.5 kN, reference speed 3,400 r/min, limiting speed 5,600 r/min, mass about 3.25 kg.
What does the /DF suffix on 31311-DF mean?
The base 31311 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 31311-DF for one bearing or the pair?
They are for the complete matched pair: C 256 kN dynamic and C0 275 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 31311 table values.
Can 31311-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 55 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 55 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.