31318 bearing: complete specifications & equivalents
The 31318 is a ISO 355 radial bearing sized 90 x 190 x 46.5 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 | 46.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 283 kN |
| Basic static load rating C0 | 315 kN |
| Fatigue load limit Pu | 35.5 kN |
| Reference speed (thermal) | 2400 rpm |
| Limiting speed (mechanical) | 3400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 5400 g |
| Manufacturer designation | SKF 31318 |
| Standard | ISO 355 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB |
| Last verified | 2026-09-26 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB) · extracted 2026-09-26
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB); 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 & 31300-series range
| Bore d | 3.543 in |
|---|---|
| Outer diameter D | 7.48 in |
| Width B | 1.831 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 50 mm |
| Smallest bore in 31300-series | 25 mm |
| Largest outer diameter in 31300-series | 320 mm |
| Width range across 31300-series | 18.25–82 mm |
| Bore position in 31300-series (smallest first) | 14 of 22 |
| Bore above smallest 31300-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 355 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 model number is decoded
For a 90 mm shaft carrying combined load, SKF lists 31318 under catalogue execution SKF 31318: one open single-row tapered roller bearing in the steep-angle heavy section of the 31300 family.Digit by digit, 31318 reads as bearing type 3 (single-row tapered roller), steep-angle heavy section series 13, and bore reference 18 resolving to 90 mm; 190 mm OD and 46.5 mm width are the matching ISO 355 boundary values. SKF lists the plain number as the basic execution; letter suffixes such as B denote a steeper contact angle and are different order numbers. At 2,400 r/min reference speed the 50.0 mm-section 31318 is governed thermally by preload and lubricant flow; grease or oil selection should be made against that value, with 3,400 r/min as the mechanical ceiling. Mounting practice for 31318: the rotating cone takes the interference fit (k5 on a 90 mm shaft), the cup slides for axial location, and reversing-thrust duty demands a paired O/X set rather than one bearing.
Typical equipment & failure modes
Common applications
- marine deck machinery shafts
- heavy industrial gearboxes and speed reducers
- large process pump and compressor shafts
- rolling-mill auxiliary drives
Known failure patterns
- cup or cone misalignment when the separable rings are not seated square during mounting
- loose cup rotation in the housing when the specified press fit is not achieved
- axial overload spalling at the roller-rib contact beyond the single-row thrust rating
- preload loss as the mounted pair relaxes, letting rollers skid and smear the raceways
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- edge loading from shaft deflection or housing misalignment
Selection pitfalls — read before you substitute
- Mount the 90 mm bore 31318 by induction heating of the cone (max 120 °C — the pressed-steel cage sets the ceiling, not the steel); driving it home through the cup or rollers brinells the tapered raceway.
- The 313 series at 90 mm bore (190×46.5 mm) has a steeper contact angle than the 302/303 families — higher axial capacity per radial load but more induced thrust and heat; do not interchange with a 30318 without re-running the pair calculation.
- O (back-to-back) pairs are stiffer against moments, X (face-to-face) pairs tolerate misalignment and thermal growth better; choosing the arrangement from the 2D drawing rather than the actual shaft thermal expansion is a common 31318 mounting error.
- A single 31318 cannot locate the shaft axially in both directions; mounting it singly on a reversing-thrust shaft leaves one direction uncontrolled — always use an O or X matched pair for bidirectional location.
- Shaft and housing fillets must clear the bearing chamfer so the 46.5 mm-wide cup seats square; use an undercut or withdrawal groove rather than an oversized radius that locks on the ring face.
- The 283/315 kN ratings are SKF catalogue 17000 values for the basic 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 and re-verify for critical drives.
- SKF lists several executions of 31318 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 31318 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What are the dimensions and catalogue data of 31318?
The SKF 31318 is a single-row tapered roller bearing with 90 mm bore, 190 mm outer diameter and 46.5 mm width (3.543 × 7.48 × 1.831 in) per ISO 355. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 283 kN, C0 315 kN, fatigue load limit Pu 35.5 kN, reference speed 2,400 r/min, limiting speed 3,400 r/min, mass about 5400 g. It is an open, separable bearing with a pressed-steel cage.
How does the 31318 bore code work?
The last two digits of 31318 are bore code 18, so 18 × 5 = 90 mm bore. The 190 mm OD and 46.5 mm width come from the ISO 355 dimension-series plan, shared with other tapered bearings of the same code.
What do the 31318 series and basic execution designations mean?
The leading 3 marks a single-row tapered roller bearing; the second digit 13 is the ISO 355 series (steep-angle heavy section). The SKF catalogue lists the ISO 355 dimension-series code after the bare number. A steeper-contact-angle variant (B suffix) is a different order number and is not interchangeable with the basic execution.
Can a single 31318 take axial load in both directions?
No — one single-row tapered roller bearing reacts thrust in one direction only, and under radial load its contact angle induces an axial force. Use two bearings as a matched pair: O (back-to-back) for a rigid, moment-resisting arrangement, X (face-to-face) where thermal expansion must be tolerated, or tandem where one-direction thrust is shared.
How does 31318 compare with a ball bearing of the same bore?
A tapered roller bearing has line contact and a steep contact angle: much higher combined axial-plus-radial capacity and shock resistance than a ball bearing of the same bore, at the cost of speed, one-direction thrust, mandatory pairing for reversing loads and a minimum axial load requirement. A ball bearing cannot be dropped into a combined-load 31318 position and vice versa — verify load direction, Fa/Fr ratio and speed before substituting.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.1 metric single-row TRB on 2026-09-26. Read our editorial & correction policy.