C3996-M bearing: complete specifications & equivalents
The C3996-M is a ISO 15 radial bearing sized 480 x 650 x 128 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 480 mm |
| Outer diameter D | 650 mm |
| Width B | 128 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 3100 kN |
| Basic static load rating C0 | 6100 kN |
| Fatigue load limit Pu | 425 kN |
| Reference speed (thermal) | 750 rpm |
| Limiting speed (mechanical) | 1000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 120000 g |
| Manufacturer designation | C 3996 M |
| Standard | ISO 15 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings |
| Last verified | 2026-09-27 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings) · extracted 2026-09-27
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings); 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 & C3900-series range
| Bore d | 18.898 in |
|---|---|
| Outer diameter D | 25.591 in |
| Width B | 5.039 in |
| ISO bore code | 96 |
| Radial section height (D−d)/2 | 85 mm |
| Smallest bore in C3900-series | 360 mm |
| Largest outer diameter in C3900-series | 2180 mm |
| Width range across C3900-series | 90–355 mm |
| Bore position in C3900-series (smallest first) | 4 of 15 |
| Bore above smallest C3900-series size | 120 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 23996 | SKF | full Dimensions and internal design equivalent — standard interchange. | Envelope-identical (480×650×128 mm) SKF spherical roller bearing SKF 23996 CA/W33 with ratings within 10 % — not a drop-in substitute: SKF 23996 CA/W33 locates the shaft axially while the CARB bearing must float; the two are designed to run as a locating/non-locating pair. |
| 23996-CAK-W33 | SKF | full Dimensions and internal design equivalent — standard interchange. | Envelope-identical (480×650×128 mm) SKF spherical roller bearing SKF 23996 CAK/W33 with ratings within 10 % — not a drop-in substitute: SKF 23996 CAK/W33 locates the shaft axially while the CARB bearing must float; the two are designed to run as a locating/non-locating pair. |
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 C3996-M model number is decoded
SKF lists C 3996 M in the dimension series 39 CARB toroidal roller bearings: the toroidal roller profile both follows tolerates angular misalignment and lets the inner ring slide axially inside the outer ring, giving free axial displacement at the non-locating position. Reading the code: C marks the CARB toroidal family, the first two digits (39) identify the ISO dimension series and the last two (96) encode the 480 mm bore; suffixes describe bore and execution. CARB bearings locate neither radially nor axially: the inner ring can walk axially inside the outer ring over the catalogue-listed axial-displacement range (s), so shaft thermal growth disappears as thrust rather than preloading the 480 mm seat. Selection arithmetic: C 3100 kN against C0 6100 kN gives a C0/C ratio of 1.97, and the 425 kN fatigue load limit Pu sets the contamination-adjusted life floor. Open executions accept relubrication — route it through the outer-ring groove on sizes that have one and purge stale grease at service intervals. Grease through the annular groove features where provided; on open executions feed lubricant past the long roller set at assembly, since the 128 mm wide cavity does not fill itself.
Typical equipment & failure modes
Common applications
- heavy industrial gearbox layshafts used as the non-locating position
- winder and reel drums in paper and steel strip plants
- paper machine drying cylinders and calender rolls with long, thermally expanding shafts
- continuous-caster guide rolls and slab-caster segments under heat growth
Known failure patterns
- roller-end and flange smearing after lubricant starvation at the long roller contacts
- thermal preloading when a shaft is located at both ends and growth has nowhere to go
- PA66 cage (TN9) softening when the sustained temperature passes the polymer limit
- brinelling of washer raceways from impact or mounting force applied through the rolling elements
- oil starvation at the sliding contact zones of large spherical roller thrust bearings on forced-feed trips
Selection pitfalls — read before you substitute
- Above 200 mm bore these bearings weigh tens of kilograms (120 kg here) — lifting gear and induction heating are mandatory, and a cocked ring scores the toroidal raceway before start-up.
- The quoted 3100/6100 kN ratings belong to this exact execution (C 3996 M); VE240 vibrating-screen variants and sealed 2CS/2NS variants have their own figures even at the same envelope.
- Do not block the axial displacement in the drawing: housing covers, labyrinth rings and snap rings must leave the catalogue float (s) free, or the bearing silently becomes a poorly located fixed bearing.
- Envelope-identical spherical roller bearings (same ISO 15 d×D×B) are not drop-in equivalents — they locate the shaft axially, while C 3996 M must float; the two are designed to be used as a pair.
- Never use C 3996 M as the locating bearing: it carries no axial load by design — the arrangement needs a separate locating spherical, tapered or angular bearing facing the thrust.
- The 3100/6100 kN ratings and 120000 g mass are SKF catalogue values transcribed from ch. 10.1 of PUB BU/P1 17000 (PDF table page 866); mounting data — axial displacement (s) and seating details — appears in the running text because the structured record carries the boundary envelope only.
Frequently asked questions
What fails first on a misapplied CARB bearing?
Blocking the designed axial float — clamping the free end or locating both shaft ends — turns thermal growth into edge loading and spalls the toroidal raceways. Cage damage and ordinary fatigue follow overload or dry running.
Which dimensions does the C 3996 M have?
A C 3996 M measures 480 mm bore × 650 mm outside diameter × 128 mm width (18.898 × 25.591 × 5.039 in). From SKF catalogue PUB BU/P1 17000: dynamic C 3100 kN, static C0 6100 kN, fatigue limit Pu 425 kN, reference speed 750 r/min, limiting speed 1,000 r/min, mass about 120000 g.
What does C 3996 M mean in SKF part numbering?
C marks CARB; 39 the dimension series; the size code gives 480 mm bore; M is the execution (cylindrical bore for direct shaft fitting, machined brass M cage). The envelope follows ISO 15 and matches spherical roller bearing outlines, but the functions differ.
Why is C 3996 M used opposite a spherical roller bearing?
The spherical bearing locates the shaft and takes thrust; the CARB bearing at the other end self-aligns but floats, absorbing thermal expansion without inducing axial load. The pair is standard on paper machine drying cylinders and long caster rolls.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 10.1 CARB toroidal roller bearings on 2026-09-27. Read our editorial & correction policy.