31306-DF bearing: complete specifications & equivalents
The 31306-DF is a ISO 355 radial bearing sized 30 x 72 x 41.5 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 30 mm |
| Outer diameter D | 72 mm |
| Width B | 41.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 100 kN |
| Basic static load rating C0 | 100 kN |
| Fatigue load limit Pu | 11.4 kN |
| Reference speed (thermal) | 5600 rpm |
| Limiting speed (mechanical) | 9500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 820 g |
| Manufacturer designation | SKF 31306/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 | 1.181 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 1.634 in |
| ISO bore code | 06 |
| Radial section height (D−d)/2 | 21 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) | 2 of 35 |
| Bore above smallest matched-df-series size | 5 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31306 | 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 31306-DF model number is decoded
Lubrication for the pair should be sized against the combined 41.5 mm width and 820 g mass: two roller sets sweep twice the contact area of a single bearing of the same bore.The SKF 31306/DF is a 30×72×41.5 mm matched tapered-roller set — two single-row bearings in face-to-face (X) matched pair arrangement, ground and shipped together with the axial clearance fixed at the factory.On the SKF nameplate, 31306-DF reads as base 31306 in a /DF matched execution — the suffix is part of the order number because a matched set is ground for a specific axial clearance and cannot be assembled from loose single bearings. 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 41.5 mm overall width of 31306-DF is the axial space the pair occupies. Catalogue mass 820 g covers both bearings and the ground spacer of 31306-DF; keep the set complete — substituting one bearing or a non-ground spacer destroys the factory clearance. Operating context for the 30 mm bore: a shaft of this diameter typically runs in the medium-bore band of industrial duty, and the 72 mm OD places the housing shoulder near 80 mm outer abutment. Load sharing in 31306-DF depends on spacer face parallelism; a cocked spacer concentrates the reversing thrust on one bearing of the pair and shows up as asymmetric raceway wear at overhaul.
Typical equipment & failure modes
Common applications
- automotive and light-truck wheel hubs
- industrial gearbox shafts and reducers
- differential and pinion drives
- belt-driven fan and blower shafts
Known failure patterns
- false brinelling on idle paired sets exposed to machine vibration
- roller large-end smearing against the cone rib after EP lubricant film failure
- cage pocket scoring when the bearing starts cold with grease of too-high base-oil viscosity
- hard-particle indentation of the tapered raceway in unfiltered oil
- electrical pitting on VFD-driven shafts without grounding protection
Selection pitfalls — read before you substitute
- Clamp the 31306-DF pair axially through the cones, never through the rollers; pressing force across the roller complement brinells the raceways of both bearings at once.
- Spacer faces must stay parallel within the set's own tolerance; a tilted spacer in 31306-DF concentrates reversing thrust on one bearing and shows up as one-sided raceway wear.
- Spacer faces must stay parallel within the set's own tolerance; a tilted spacer in 31306-DF concentrates reversing thrust on one bearing and shows up as one-sided raceway wear.
- The 100/100 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 31306/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 31306-DF?
The SKF 31306/DF is a matched pair of single-row tapered roller bearings in face-to-face (X) matched pair arrangement with 30 mm bore, 72 mm outer diameter and 41.5 mm overall width (1.181 × 2.835 × 1.634 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 100 kN, C0 100 kN, fatigue load limit Pu 11.4 kN, reference speed 5,600 r/min, limiting speed 9,500 r/min, mass about 0.82 kg.
What does the /DF suffix on 31306-DF mean?
The base 31306 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 31306-DF for one bearing or the pair?
They are for the complete matched pair: C 100 kN dynamic and C0 100 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 31306 table values.
Can 31306-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 30 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 30 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.