31305 bearing: complete specifications & equivalents
The 31305 is a ISO 355 radial bearing sized 25 x 62 x 18.25 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 25 mm |
| Outer diameter D | 62 mm |
| Width B | 18.25 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 46.6 kN |
| Basic static load rating C0 | 40 kN |
| Fatigue load limit Pu | 4.4 kN |
| Reference speed (thermal) | 8500 rpm |
| Limiting speed (mechanical) | 11000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 270 g |
| Manufacturer designation | SKF 31305 |
| 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 | 0.984 in |
|---|---|
| Outer diameter D | 2.441 in |
| Width B | 0.719 in |
| ISO bore code | 05 |
| Radial section height (D−d)/2 | 18.5 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) | 1 of 22 |
| Bore above smallest 31300-series size | 0 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31305 | 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 31305 model number is decoded
SKF 31305 (SKF 31305) is the steep-angle heavy section tapered roller choice for a 25 mm shaft — one row of tapered rollers on an asymmetric raceway inside the 62×18.25 mm ISO 355 envelope.Digit by digit, 31305 reads as bearing type 3 (single-row tapered roller), steep-angle heavy section series 13, and bore reference 05 resolving to 25 mm; 62 mm OD and 18.25 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 8,500 r/min reference speed the 18.5 mm-section 31305 is governed thermally by preload and lubricant flow; grease or oil selection should be made against that value, with 11,000 r/min as the mechanical ceiling. Because the contact line is tapered, one 31305 reacts thrust in a single direction; bidirectional shafts need an O or X pair, and a rotating cone on a 25 mm shaft typically takes a k5 seat with an H7 housing bore.
Typical equipment & failure modes
Common applications
- power-tool gear heads
- small automotive wheel hubs and trailer axles
- light-duty gearbox input/output shafts
- electric-motor pinion shafts
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
- roller large-end smearing against the cone rib after EP lubricant film failure
- false brinelling on idle paired sets exposed to machine vibration
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- electrical pitting on VFD-driven shafts without grounding protection
Selection pitfalls — read before you substitute
- At a 25 mm bore the thin cone and cup are easily distorted by an over-tight shaft nut; check seat runout (target Ra ≤ 0.8 µm) and torque the locknut progressively — a pinched 31305 shows up as gearbox vibration long before it fails.
- The 313 series at 25 mm bore (62×18.25 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 30305 without re-running the pair calculation.
- Setting is a design value, not an assembly feel: excessive preload in the 31305 pair raises operating temperature and can trigger thermal runaway, while too little lets the rollers skid and smear the raceway under light load.
- Do not mix brands or executions inside one 31305 pair — matched sets are ground for a specific setting, and pairing a SKF basic unit with a different suffix variant will not share the setting evenly.
- Open 31305 units need application-supplied sealing and a defined EP lubricant supply; the roller-rib contact is the first to fail when the additive film breaks down.
- The 46.6/40 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 31305 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 31305 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What are the dimensions and catalogue data of 31305?
The SKF 31305 is a single-row tapered roller bearing with 25 mm bore, 62 mm outer diameter and 18.25 mm width (0.984 × 2.441 × 0.719 in) per ISO 355. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 46.6 kN, C0 40 kN, fatigue load limit Pu 4.4 kN, reference speed 8,500 r/min, limiting speed 11,000 r/min, mass about 270 g. It is an open, separable bearing with a pressed-steel cage.
How does the 31305 bore code work?
The last two digits of 31305 are bore code 05, so 05 × 5 = 25 mm bore. The 62 mm OD and 18.25 mm width come from the ISO 355 dimension-series plan, shared with other tapered bearings of the same code.
What do the 31305 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 31305 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 31305 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 31305 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.