31320T125X-DB bearing: complete specifications & equivalents
The 31320T125X-DB is a ISO 355 radial bearing sized 100 x 215 x 125 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 100 mm |
| Outer diameter D | 215 mm |
| Width B | 125 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 685 kN |
| Basic static load rating C0 | 930 kN |
| Fatigue load limit Pu | 102 kN |
| Reference speed (thermal) | 1700 rpm |
| Limiting speed (mechanical) | 3000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 19000 g |
| Manufacturer designation | SKF 31320T125 X/DB |
| 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-db-series range
| Bore d | 3.937 in |
|---|---|
| Outer diameter D | 8.465 in |
| Width B | 4.921 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 57.5 mm |
| Smallest bore in matched-db-series | 35 mm |
| Largest outer diameter in matched-db-series | 480 mm |
| Width range across matched-db-series | 41.5–288 mm |
| Bore position in matched-db-series (smallest first) | 14 of 30 |
| Bore above smallest matched-db-series size | 65 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 31320T125X | 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 31320T125X-DB model number is decoded
Assembly datum check: verify the 125 mm width against the drawing before clamping — the width is the assembled result and the quickest field check that the correct execution of 31320T125X-DB is on the shaft. When a matched /DB set like 31320T125X-DB is replaced, replace the whole set: mixing a new bearing with a worn partner from the old set leaves the clearance and load sharing of the pair undefined. A matched /DB set needs no setting adjustment at mounting: the clearance is built in; the assembler's job is clean seats, correct fits (k5 on a 100 mm rotating shaft) and square abutments.For a 100 mm shaft carrying reversing axial load, SKF lists 31320T125X-DB under catalogue execution SKF 31320T125 X/DB: a factory-matched back-to-back (O) matched pair tapered-roller pair, set and measured as one unit.Reading the designation: 31320T125 X is the ISO 355 single-row base bearing (100 mm bore), and the suffix /DB marks the matched-set execution — arrangement, spacer grinding and factory clearance class. The pair envelope is 100×215×125 mm; the width covers both bearings of the set. Back-to-back matching puts the large rib ends outward — the stiffest arrangement for moment load, but one that converts shaft thermal growth into preload change; the factory setting of 31320T125X-DB already accounts for the expected temperature gradient across the 125 mm pair width. Dividing the pair C 685 kN by the 100 mm bore gives 6.85 kN per millimetre of journal for the complete arrangement — a density metric that compares matched sets across the back-to-back (O) matched pair family.
Typical equipment & failure modes
Common applications
- marine deck machinery shafts
- heavy industrial gearboxes and speed reducers
- large process pump and compressor shafts
- heavy industrial gearboxes and speed reducers
Known failure patterns
- preload loss as the mounted pair relaxes, letting rollers skid and smear the raceways
- uneven load sharing in a pair when spacer faces are not parallel to the bore
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- fretting corrosion on a loose rotating shaft seat
- rib-roller contact scoring from loss of the EP additive film
Selection pitfalls — read before you substitute
- O and X arrangements are not interchangeable by turning the set around: 31320T125X-DB in back-to-back (O) matched pair arrangement has its load-line geometry fixed — specify the arrangement from the shaft thermal and stiffness analysis.
- Setting is built into 31320T125X-DB; the classic field error is re-adjusting a matched pair as if it were two loose single bearings, which destroys the /DB clearance class.
- Spacer faces must stay parallel within the set's own tolerance; a tilted spacer in 31320T125X-DB concentrates reversing thrust on one bearing and shows up as one-sided raceway wear.
- The 685/930 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 31320T125 X/DB designation when purchasing — base-number-only orders are ambiguous across executions and variants.
Frequently asked questions
What are the dimensions and catalogue data of 31320T125X-DB?
The SKF 31320T125 X/DB is a matched pair of single-row tapered roller bearings in back-to-back (O) matched pair arrangement with 100 mm bore, 215 mm outer diameter and 125 mm overall width (3.937 × 8.465 × 4.921 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 685 kN, C0 930 kN, fatigue load limit Pu 102 kN, reference speed 1,700 r/min, limiting speed 3,000 r/min, mass about 19.00 kg.
What does the /DB suffix on 31320T125X-DB mean?
The base 31320T125 X is the ISO 355 single-row bearing; the /DB suffix marks the matched-set execution — the arrangement (back-to-back (O)), 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 31320T125X-DB for one bearing or the pair?
They are for the complete matched pair: C 685 kN dynamic and C0 930 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 31320T125 X table values.
Can 31320T125X-DB 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 100 mm shaft) and axial clamping through the cones; re-setting in the field destroys the matched clearance class.
When should a back-to-back (O) matched set be chosen?
Choose the back-to-back (O) set where moment stiffness dominates — pinion supports, gearbox output shafts, crane sheaves. The diverging load lines give the widest effective spread at the 100 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.