30311-DF bearing: complete specifications & equivalents
The 30311-DF is a ISO 355 radial bearing sized 55 x 120 x 63 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 | 63 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 302 kN |
| Basic static load rating C0 | 325 kN |
| Fatigue load limit Pu | 39 kN |
| Reference speed (thermal) | 3800 rpm |
| Limiting speed (mechanical) | 5600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 3250 g |
| Manufacturer designation | SKF 30311/DF |
| 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-df-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 4.724 in |
| Width B | 2.48 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in matched-df-series | 25 mm |
| Largest outer diameter in matched-df-series | 540 mm |
| Width range across matched-df-series | 34.5–280 mm |
| Bore position in matched-df-series (smallest first) | 7 of 35 |
| Bore above smallest matched-df-series size | 30 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30311 | 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. |
| 30311-NTN | NTN | verify Commonly quoted cross reference; confirm against the target catalog before ordering. | Model-number interchange per ISO 15; confirm dimensions, sealing and ratings in the supplier catalogue. |
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 30311-DF model number is decoded
Load system: C 302 kN against C0 325 kN gives a 1.08 balance, and 5.49 kN of dynamic capacity per millimetre of the 55 mm bore is the density figure to compare against neighbouring sizes. Inspection shorthand: at overhaul, mark both bearings and the spacer of 30311-DF before disassembly — the set is a matched system, and re-assembling with one component reversed changes the factory setting. Lubrication for the pair should be sized against the combined 63 mm width and 3250 g mass: two roller sets sweep twice the contact area of a single bearing of the same bore.In SKF catalogue PUB BU/P1 17000, 30311-DF appears as SKF 30311/DF: a matched face-to-face (X) matched pair pair for a 55 mm shaft, rated as a set at C 302 kN and C0 325 kN.Reading the designation: 30311 is the ISO 355 single-row base bearing (55 mm bore), and the suffix /DF marks the matched-set execution — arrangement, spacer grinding and factory clearance class. The pair envelope is 55×120×63 mm; the width covers both bearings of the set. Face-to-face matching puts the small rib ends outward, so the pressure cones cross inside the pair; 30311-DF therefore runs cooler where the shaft expands axially, at the price of lower moment stiffness than an O-arrangement of the same 55 mm bore. Dividing the pair C 302 kN by the 55 mm bore gives 5.49 kN per millimetre of journal for the complete arrangement — a density metric that compares matched sets across the face-to-face (X) matched pair family.
Typical equipment & failure modes
Common applications
- pump and compressor shafts
- machine-tool spindles
- belt-driven fan and blower shafts
- machine-tool spindles
Known failure patterns
- roller large-end smearing against the cone rib after EP lubricant film failure
- roller large-end smearing against the cone rib after EP lubricant film failure
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- edge loading from shaft deflection or housing misalignment
- grease degradation after long shelf storage without rotation or re-greasing
Selection pitfalls — read before you substitute
- Replace 30311-DF as a complete set: pairing a new bearing with a worn partner leaves the clearance undefined even when the designation matches.
- Setting is built into 30311-DF; the classic field error is re-adjusting a matched pair as if it were two loose single bearings, which destroys the /DF clearance class.
- A matched /DF set is ground as one system: never separate the two bearings of 30311-DF or swap the spacer — the factory clearance is lost the moment the set is broken.
- The 302/325 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 30311/DF designation when purchasing — base-number-only orders are ambiguous across executions and variants.
Frequently asked questions
What are the dimensions and catalogue data of 30311-DF?
The SKF 30311/DF is a matched pair of single-row tapered roller bearings in face-to-face (X) matched pair arrangement with 55 mm bore, 120 mm outer diameter and 63 mm overall width (2.165 × 4.724 × 2.48 in). From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 302 kN, C0 325 kN, fatigue load limit Pu 39 kN, reference speed 3,800 r/min, limiting speed 5,600 r/min, mass about 3.25 kg.
What does the /DF suffix on 30311-DF mean?
The base 30311 is the ISO 355 single-row bearing; the /DF suffix marks the matched-set execution — the arrangement (face-to-face (X)), 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 30311-DF for one bearing or the pair?
They are for the complete matched pair: C 302 kN dynamic and C0 325 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 30311 table values.
Can 30311-DF 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 55 mm shaft) and axial clamping through the cones; re-setting in the field destroys the matched clearance class.
When should a face-to-face (X) matched set be chosen?
Choose the face-to-face (X) set where the shaft grows thermally or alignment is imperfect — the converging load lines tolerate deflection. It is the default choice for wheel hubs and general gearbox shafts at the 55 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.