31311 bearing: complete specifications & equivalents
The 31311 is a ISO 355 radial bearing sized 55 x 120 x 31.5 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 | 31.5 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 149 kN |
| Basic static load rating C0 | 137 kN |
| Fatigue load limit Pu | 16.6 kN |
| Reference speed (thermal) | 4300 rpm |
| Limiting speed (mechanical) | 5600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1550 g |
| Manufacturer designation | SKF 31311 |
| 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 | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 1.24 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 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) | 7 of 22 |
| Bore above smallest 31300-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 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 31311 model number is decoded
For a 55 mm shaft carrying combined load, SKF lists 31311 under catalogue execution SKF 31311: one open single-row tapered roller bearing in the steep-angle heavy section of the 31300 family.The code breaks down as type prefix 3 (tapered roller), series 13 (the steep-angle heavy section), and bore code 11 = 55 mm; dimensions 55×120×31.5 mm therefore match the ISO 355 envelope. 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 4,300 r/min reference speed the 32.5 mm-section 31311 is governed thermally by preload and lubricant flow; grease or oil selection should be made against that value, with 5,600 r/min as the mechanical ceiling. Mounting practice for 31311: the rotating cone takes the interference fit (k5 on a 55 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
- axle-boxes in material-handling equipment
- automotive and light-truck wheel hubs
- industrial gearbox shafts and reducers
- differential and pinion 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
- 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
- brinelling from pressing the cone or cup home through the rollers
Selection pitfalls — read before you substitute
- On this 55 mm bore, interference and temperature rise consume clearance inside a preloaded pair; calculate the residual clearance after mounting and at operating temperature — an over-tight 31311 pair heats, loses setting control and smears the roller-rib contact.
- The 313 series at 55 mm bore (120×31.5 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 30311 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 31311 mounting error.
- A single 31311 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 31.5 mm-wide cup seats square; use an undercut or withdrawal groove rather than an oversized radius that locks on the ring face.
- The 149/137 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 31311 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 31311 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What are the dimensions and catalogue data of 31311?
The SKF 31311 is a single-row tapered roller bearing with 55 mm bore, 120 mm outer diameter and 31.5 mm width (2.165 × 4.724 × 1.24 in) per ISO 355. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 149 kN, C0 137 kN, fatigue load limit Pu 16.6 kN, reference speed 4,300 r/min, limiting speed 5,600 r/min, mass about 1550 g. It is an open, separable bearing with a pressed-steel cage.
How does the 31311 bore code work?
The last two digits of 31311 are bore code 11, so 11 × 5 = 55 mm bore. The 120 mm OD and 31.5 mm width come from the ISO 355 dimension-series plan, shared with other tapered bearings of the same code.
What do the 31311 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 31311 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 31311 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 31311 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.