31318-DF bearing: complete specifications & equivalents
The 31318-DF is a ISO 355 radial bearing sized 90 x 190 x 93 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 90 mm |
| Outer diameter D | 190 mm |
| Width B | 93 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 486 kN |
| Basic static load rating C0 | 630 kN |
| Fatigue load limit Pu | 71 kN |
| Reference speed (thermal) | 1900 rpm |
| Limiting speed (mechanical) | 3400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 11500 g |
| Manufacturer designation | SKF 31318/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 | 3.543 in |
|---|---|
| Outer diameter D | 7.48 in |
| Width B | 3.661 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 50 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) | 14 of 35 |
| Bore above smallest matched-df-series size | 65 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31318 | 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 31318-DF model number is decoded
On the SKF nameplate, 31318-DF reads as base 31318 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. Face-to-face matching puts the small rib ends outward, so the pressure cones cross inside the pair; 31318-DF therefore runs cooler where the shaft expands axially, at the price of lower moment stiffness than an O-arrangement of the same 90 mm bore. The C0/C balance of the pair is about 1.30; combined with the 71 kN fatigue limit this frames a set sized for reversing combined load on a 90 mm shaft rather than for pure radial duty. Assembly datum check: verify the 93 mm width against the drawing before clamping — the width is the assembled result and the quickest field check that the correct execution of 31318-DF is on the shaft. Inspection shorthand: at overhaul, mark both bearings and the spacer of 31318-DF before disassembly — the set is a matched system, and re-assembling with one component reversed changes the factory setting. Do not separate 31318-DF into single-bearing service stock — as individual bearings the components are not interchangeable with catalogue single-row executions because the rings are ground for the set.31318-DF is a matched pair of single-row tapered roller bearings arranged face-to-face (X) matched pair, supplied by SKF in SKF catalogue PUB BU/P1 17000 as one factory-set unit: the two bearings, spacers and setting are matched together and must not be mixed with other sets.
Typical equipment & failure modes
Common applications
- rolling-mill auxiliary drives
- crane sheave and hoist gearboxes
- paper-machine and printing rolls
- paper-machine and printing rolls
Known failure patterns
- thermal preload runaway in an O-arrangement pair when inner-ring heat expands the setting
- axial overload spalling at the roller-rib contact beyond the single-row thrust rating
- cage pocket scoring when the bearing starts cold with grease of too-high base-oil viscosity
- rolling-contact fatigue spalling after the rated L10 life is exceeded
- rib-roller contact scoring from loss of the EP additive film
Selection pitfalls — read before you substitute
- Clamp the 31318-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 31318-DF concentrates reversing thrust on one bearing and shows up as one-sided raceway wear.
- A matched /DF set is ground as one system: never separate the two bearings of 31318-DF or swap the spacer — the factory clearance is lost the moment the set is broken.
- The 486/630 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 31318/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 31318-DF?
The SKF 31318/DF is a matched pair of single-row tapered roller bearings in face-to-face (X) matched pair arrangement with 90 mm bore, 190 mm outer diameter and 93 mm overall width (3.543 × 7.48 × 3.661 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 486 kN, C0 630 kN, fatigue load limit Pu 71 kN, reference speed 1,900 r/min, limiting speed 3,400 r/min, mass about 11.50 kg.
What does the /DF suffix on 31318-DF mean?
The base 31318 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 31318-DF for one bearing or the pair?
They are for the complete matched pair: C 486 kN dynamic and C0 630 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 31318 table values.
Can 31318-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 90 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 90 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.