30208 bearing: complete specifications & equivalents
The 30208 is a ISO 355 radial bearing sized 40 x 80 x 19.75 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | SKF |
| Bore diameter d | 40 mm |
| Outer diameter D | 80 mm |
| Width B | 19.75 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel, stamped ribbon (J-type) |
| Basic dynamic load rating C | 75.8 kN |
| Basic static load rating C0 | 68 kN |
| Fatigue load limit Pu | 7.65 kN |
| Reference speed (thermal) | 7000 rpm |
| Limiting speed (mechanical) | 8500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 420 g |
| Manufacturer designation | SKF 30208 |
| 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 & 30200-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 3.15 in |
| Width B | 0.778 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 20 mm |
| Smallest bore in 30200-series | 15 mm |
| Largest outer diameter in 30200-series | 580 mm |
| Width range across 30200-series | 11.75–104 mm |
| Bore position in 30200-series (smallest first) | 8 of 37 |
| Bore above smallest 30200-series size | 25 mm |
Mounting, setting & life for 30208
Fits & mounting
- Tapered bearings are separable: press the cup square into the housing and fit the cone on the shaft — usually an interference fit on both seats in wheel/hub positions.
- Mount the cone by induction heating (max 120 °C); never strike the cage or rollers directly.
- Shaft and housing shoulders must clear the ring chamfers so the cone and cup seat fully against their faces.
Setting — the step deep-groove bearings never need
- After seating, set the assembly to a defined end play or preload with the locknut/shim arrangement; locknut torque seats the parts — it is not the final adjustment.
- General free-running positions: back the nut off while measuring with a dial indicator to a small end play (commonly around 0.05–0.15 mm for medium metric hubs — follow the OEM value).
- Pinions and stiff arrangements run a controlled preload; too much preload is the classic cause of early spalling and heat.
- Sealed factory-set units exist for specific designations — the open 30208 assumes the application sets and lubricates it.
Lubrication
Open TRBs are lubricated by the application. Fill the bearing with grease (typically around one third to one half of the free cavity — overpacking a TRB causes churning heat) and provide a relubrication path; intervals depend on contamination and temperature, not on catalogue rating alone.
Why the equivalent load matters more here
TRBs carry combined radial and axial loads, so the dynamic equivalent load P is computed with the bearing's e, X and Y factors for the actual thrust ratio — using the radial load alone over-estimates life badly.
Worked L10 life example (illustrative duty)
For roller bearings the life exponent is p = 10/3: L10h = (C/P)10/3 · 106 / (60·n). Taking an example equivalent load P = 15.2 kN (20% of C) at n = 1,500 r/min — substitute the real P from the X/Y calculation:
C = 75.8 kN → L10h ≈ 2,375 hours
Choosing a series at the same 40 mm bore
| Series | Open execution | OD × width T | C (kN) | C0 (kN) | Limiting speed (r/min) |
|---|---|---|---|---|---|
| 320xx | 32008 | 68 × 19 | 63.0 | 71.0 | 12,800 |
| 302xx | 30208 | 80 × 19.75 | 75.8 | 68.0 | 8,500 |
| 322xx | 32208 | 80 × 24.75 | 94.0 | 94.0 | 11,200 |
| 332xx | 33208 | 80 × 32 | 128.0 | 132.0 | 8,500 |
| 303xx | 30308C | 90 × 25.25 | 92.0 | 87.0 | 4,200 |
| 323xx | 32308C | 90 × 35.25 | 122.0 | 140.0 | 4,200 |
| 313xx | 31308 | 90 × 25.25 | 91.1 | 81.5 | 7,500 |
Different series at the same bore are not drop-in swaps — OD, width and contact angle all change — and a cone number alone never identifies a complete set. Verify matches per the cross-reference levels guide; envelope variants are on the 40×80×19.75 envelope page.
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 30208 | ISO 15 | full Dimensions and internal design equivalent — standard interchange. | ISO 15 boundary-dimension envelope; standard interchange — confirm clearance class and precision with the supplier. |
| 30208-NTN | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×80×19.75 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
| 30208R | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Flanged-cup variant of this base bearing: same d/D/T boundary, different housing location concept — not a drop-in substitute where the flange is the axial register. |
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 30208 model number is decoded
The SKF 30208 is a 40×80×19.75 mm single-row tapered roller bearing — the standard section entry in the 30200 series, with an asymmetric raceway cut for thrust capacity and separable mounting.The code breaks down as type prefix 3 (tapered roller), series 0 (the standard section), and bore code 08 = 40 mm; dimensions 40×80×19.75 mm therefore match the ISO 355 envelope. SKF lists the plain number as the basic execution; letter suffixes such as B denote a steeper contact angle and are different order numbers. Speed planning uses two different ceilings: 7,000 r/min thermal reference and 8,500 r/min mechanical limiting speed. Specify pairs rather than single units wherever thrust reverses: the tapered contact of 30208 generates an induced axial load under radial force, and an unpaired bearing on a reversing shaft will run slack and fret its seat.
Typical equipment & failure modes
Common applications
- industrial gearbox shafts and reducers
- differential and pinion drives
- pump and compressor shafts
- machine-tool spindles
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
- preload loss as the mounted pair relaxes, letting rollers skid and smear the raceways
- pressed-steel cage wear or fracture after prolonged running above the limiting speed
- rolling-contact fatigue spalling after the rated L10 life is exceeded
Selection pitfalls — read before you substitute
- On this 40 mm bore, interference and temperature rise consume clearance inside a preloaded pair; calculate the residual clearance after mounting and at operating temperature — an over-tight 30208 pair heats, loses setting control and smears the roller-rib contact.
- The 302 series at 40 mm bore (80×19.75 mm) is the standard tapered-roller envelope; stepping to a 32208 or 32308 changes OD, width and heat generation — it is not a drop-in swap when the housing and speed are fixed.
- A single 30208 cannot locate the shaft axially in both directions; mounting it singly on a reversing-thrust shaft leaves one direction uncontrolled — always use an O or X matched pair for bidirectional location.
- O (back-to-back) pairs are stiffer against moments, X (face-to-face) pairs tolerate misalignment and thermal growth better; choosing the arrangement from the 2D drawing rather than the actual shaft thermal expansion is a common 30208 mounting error.
- The pressed-steel cage is rated for standard industrial service; sustained running above the limiting speed or with degraded lubricant wears the cage pockets — inspect the cage at every relubrication interval.
- The 75.8/68 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 30208 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 30208 designation when purchasing and match the execution to the mounting arrangement.
Frequently asked questions
What are the dimensions and catalogue data of 30208?
The SKF 30208 is a single-row tapered roller bearing with 40 mm bore, 80 mm outer diameter and 19.75 mm width (1.575 × 3.15 × 0.778 in) per ISO 355. From SKF catalogue PUB BU/P1 17000: basic dynamic load rating C 75.8 kN, C0 68 kN, fatigue load limit Pu 7.65 kN, reference speed 7,000 r/min, limiting speed 8,500 r/min, mass about 420 g. It is an open, separable bearing with a pressed-steel cage.
How does the 30208 bore code work?
The last two digits of 30208 are bore code 08, so 08 × 5 = 40 mm bore. The 80 mm OD and 19.75 mm width come from the ISO 355 dimension-series plan, shared with other tapered bearings of the same code.
What do the 30208 series and basic execution designations mean?
The leading 3 marks a single-row tapered roller bearing; the second digit 0 is the ISO 355 series (standard 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 30208 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 30208 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 30208 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.