3984-3920 bearing: complete specifications & equivalents
The 3984-3920 is a ISO 355 radial bearing sized 65.088 x 112.712 x 30.162 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 65.088 mm |
| Outer diameter D | 112.712 mm |
| Width B | 30.162 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 152 kN |
| Basic static load rating C0 | 183 kN |
| Fatigue load limit Pu | 21.2 kN |
| Reference speed (thermal) | 4800 rpm |
| Limiting speed (mechanical) | 5600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1150 g |
| Manufacturer designation | SKF 3984/3920 |
| Standard | ISO 355 |
| Catalog version | SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.2 inch single-row TRB |
| Last verified | 2026-09-28 |
Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.2 inch single-row TRB) · extracted 2026-09-28
Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.2 inch 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 & 3900-series range
| Bore d | 2.563 in |
|---|---|
| Outer diameter D | 4.437 in |
| Width B | 1.187 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 23.8 mm |
| Smallest bore in 3900-series | 65.088 mm |
| Largest outer diameter in 3900-series | 112.712 mm |
| Width range across 3900-series | 30.162–30.162 mm |
| Bore position in 3900-series (smallest first) | 1 of 1 |
| Bore above smallest 3900-series size | 0 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 3984-3925 | 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. |
| 3984-3920 | Timken | full Dimensions and internal design equivalent — standard interchange. | Same inch-series cone/cup boundary envelope (d/D/T); load ratings and speed limits are brand-specific and may differ. |
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 3984-3920 model number is decoded
The SKF catalogue adds the ISO 355 dimension-series code after the bare number (e.g. ); it is the dimensional series, not a separate part number. Selection arithmetic: the C0/C ratio is about 1.20 (static 183 kN against dynamic 152 kN), typical of a tapered roller sized for axial capacity, and the 21.2 kN fatigue load limit Pu is the equivalent-load floor used in the life calculation. Specify pairs rather than single units wherever thrust reverses: the tapered contact of 3984 generates an induced axial load under radial force, and an unpaired bearing on a reversing shaft will run slack and fret its seat. Cross-section geometry: the 23.8 mm half-section ((112.712−65.088)/2) of this 39800-series unit places the roller large-end pitch diameter at roughly 88 mm, and the 30.162 mm axial width is split between cone (17 mm) and cup rib (14 mm) — a geometry that sets the contact angle and, with the 1150 g rotating cone mass, the critical speed at which cage-roller imbalance begins. A single-row inch tapered bearing is quoted as a cone/cup pair because the boundary dimensions belong to the combination, not to either half alone: in 3984 the 3984 cone contributes the 65.088 mm bore and roller set, the 3920 cup contributes the 112.712 mm OD raceway, and the assembled 30.162 mm width is the catalogue value.In SKF catalogue PUB BU/P1 17000, 3984 appears as SKF 3984/3920: an open, single-row tapered roller bearing in the 3900-series, supplied with a pressed-steel cage as standard.Reading the designation: 3984 follows the Timken-style inch convention — the cone (inner ring with rollers) and cup (outer ring) are quoted as a pair separated by a slash, and the 3900-series code identifies the dimensional series. The 65.088 mm bore, 112.712 mm OD and 30.162 mm width are the metric equivalents of the inch boundary dimensions.
Typical equipment & failure modes
Common applications
- construction machinery drives
- marine deck machinery shafts
- heavy industrial gearboxes and speed reducers
- rolling-mill auxiliary drives
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
- axial overload spalling at the roller-rib contact beyond the single-row thrust rating
- axial overload spalling at the roller-rib contact beyond the single-row thrust rating
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- grease degradation after long shelf storage without rotation or re-greasing
Selection pitfalls — read before you substitute
- Mount the 65.088 mm bore 3984 by induction heating of the cone (max 120 °C — the pressed-steel cage sets the ceiling, not the steel); driving it home through the cup or rollers brinells the tapered raceway.
- The 320 series at 65.088 mm bore (112.712×30.162 mm) is the low-friction, higher-speed section; it carries less thrust than a 302 of the same bore, so verify the axial load share before swapping.
- Setting is a design value, not an assembly feel: excessive preload in the 3984 pair raises operating temperature and can trigger thermal runaway, while too little lets the rollers skid and smear the raceway under light load.
- At the 152 kN rating of 3984, preload class changes stiffness by tens of percent but also heat generation; select light preload for the 5,600 r/min speed end and heavier preload only where moment stiffness dominates.
- Open 3984 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 152/183 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 3984 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 3984/3920 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What do the cone and cup numbers in 3984 mean?
The cone number (before the slash) identifies the inner ring, rollers and cage; the cup number (after the slash) identifies the outer ring. Both are quoted together because a single-row tapered roller bearing is a matched separable pair — the cone and cup are ground to work together and are not interchangeable with arbitrary other parts. The series prefix (3900-series) groups sizes that share the same boundary-dimension plan.
Can a single 3984 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 3984 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 3984 position and vice versa — verify load direction, Fa/Fr ratio and speed before substituting.
What shaft and housing fits suit 3984?
For a rotating shaft under normal load, seat the cone on a k5 shaft fit; the cup is usually a loose-to-transition fit in the housing so it can creep slightly and distribute wear. Chamfer and shoulder diameters must clear the bearing rings so the 30.162 mm-wide cup seats square; the mounting setting (end play or preload) is set by the axial position of the cup relative to the cone.
Is 3984 interchangeable with other brands?
Inch-series tapered roller bearings follow a long-standing industry boundary plan, so cones and cups of the same basic number are generally dimensionally interchangeable across manufacturers. However, internal geometry, cage design and load ratings differ by brand, so for paired or precision applications keep both halves of the set from one manufacturer — or re-verify ratings and setting when mixing.
Reviewed & verified by the MPN Base engineering desk against source catalog SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.2 inch single-row TRB on 2026-09-28. Read our editorial & correction policy.