31306 bearing: complete specifications & equivalents
The 31306 is a ISO 355 radial bearing sized 30 x 72 x 20.75 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 | 20.75 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 58.3 kN |
| Basic static load rating C0 | 50 kN |
| Fatigue load limit Pu | 5.7 kN |
| Reference speed (thermal) | 7500 rpm |
| Limiting speed (mechanical) | 9500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 390 g |
| Manufacturer designation | SKF 31306 |
| 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 | 1.181 in |
|---|---|
| Outer diameter D | 2.835 in |
| Width B | 0.817 in |
| ISO bore code | 06 |
| Radial section height (D−d)/2 | 21 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) | 2 of 22 |
| Bore above smallest 31300-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 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 31306 model number is decoded
Ordering number SKF 31306 in SKF catalogue PUB BU/P1 17000 denotes a single-row tapered roller bearing for a 30 mm shaft, steep-angle heavy section, with an open pressed-steel-cage execution and one-direction axial capacity.Numbering ties the bearing to its envelope: 31306 means tapered-roller type 3, steep-angle heavy section series 13, 30 mm bore — which is why the 72×20.75 mm outline swaps dimensionally with other ISO 355 bearings of the same code. SKF lists the plain number as the basic execution; letter suffixes such as B denote a steeper contact angle and are different order numbers. Speed planning uses two different ceilings: 7,500 r/min thermal reference and 9,500 r/min mechanical limiting speed. For a 30 mm shaft the usual cone seat is k5 with an H7 housing when the inner ring rotates; arrange two 31306 bearings as a set for two-direction location and set clearance from the load diagram, never from assembly feel.
Typical equipment & failure modes
Common applications
- industrial gearbox shafts and reducers
- differential and pinion drives
- pump and compressor shafts
- machine-tool spindles
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
- preload loss as the mounted pair relaxes, letting rollers skid and smear the raceways
- 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
- edge loading from shaft deflection or housing misalignment
Selection pitfalls — read before you substitute
- On this 30 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 31306 pair heats, loses setting control and smears the roller-rib contact.
- The 313 series at 30 mm bore (72×20.75 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 30306 without re-running the pair calculation.
- A single 31306 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.
- 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 31306 mounting error.
- Shaft and housing fillets must clear the bearing chamfer so the 20.75 mm-wide cup seats square; use an undercut or withdrawal groove rather than an oversized radius that locks on the ring face.
- The 58.3/50 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 31306 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 31306 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What are the dimensions and catalogue data of 31306?
The SKF 31306 is a single-row tapered roller bearing with 30 mm bore, 72 mm outer diameter and 20.75 mm width (1.181 × 2.835 × 0.817 in) per ISO 355. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 58.3 kN, C0 50 kN, fatigue load limit Pu 5.7 kN, reference speed 7,500 r/min, limiting speed 9,500 r/min, mass about 390 g. It is an open, separable bearing with a pressed-steel cage.
How does the 31306 bore code work?
The last two digits of 31306 are bore code 06, so 06 × 5 = 30 mm bore. The 72 mm OD and 20.75 mm width come from the ISO 355 dimension-series plan, shared with other tapered bearings of the same code.
What do the 31306 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 31306 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 31306 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 31306 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.