NN3008K bearing: complete specifications & equivalents
The NN3008K is a ISO 15 radial bearing sized 40 x 68 x 21 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 40 mm |
| Outer diameter D | 68 mm |
| Width B | 21 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 48 kN |
| Basic static load rating C0 | 55.5 kN |
| Fatigue load limit Pu | 6.75 kN |
| Limiting speed (mechanical) | 9700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 303 g |
| Manufacturer designation | NTN NN3008K |
| Standard | ISO 15 |
| Catalog version | NTN Ball and Roller Bearings CAT.No.2203E |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); NTN® is a trademark of NTN Corporation, used here for identification only — mpnbase is not an authorized NTN distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at ntnglobal.com.
Dimensions in inches & NN3000-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 2.677 in |
| Width B | 0.827 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 14 mm |
| Smallest bore in NN3000-series | 25 mm |
| Largest outer diameter in NN3000-series | 680 mm |
| Width range across NN3000-series | 16–163 mm |
| Bore position in NN3000-series (smallest first) | 4 of 40 |
| Bore above smallest NN3000-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NN3008K | 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 NN3008K model number is decoded
NN3008K is the standard section of the NTN NN3000 dimension series for a 40 mm shaft — 48 kN of basic dynamic capacity in a 303 g, open bearing. The leading NN defines the rib arrangement (double row, ribbed inner ring, separable outer); the dimension-series digits and the two-digit bore code resolve to 40 mm, with 68 mm OD and 21 mm width from the ISO 15 general plan. The roller-set pitch sits inside the 14.0 mm radial section between the 40 mm bore and 68 mm OD; NTN prints Fw/Ew raceway diameters only for selected executions. Mass 303 g for the 40×68×21 mm NN3008K execution covers the pressed-steel cage and full roller complement; substitute on mass plus rating, not envelope alone. On NN arrangements confirm which ring is separable before heating: forcing the ribbed ring off over the roller complement damages the cage and rib faces.
Typical equipment & failure modes
Common applications
- coordinate-measuring and semiconductor-equipment drives
- machine-tool main spindles requiring high radial stiffness
- precision gearbox and indexing-drive shafts
- high-rpm motorised grinding and milling spindles
Known failure patterns
- roller smearing (microwelding) at start-up before the oil film builds under insufficient radial load
- cage distortion after a mounting blow carried through the roller set
- roller-end and raceway scoring from inadequate oil flow under heavy radial load
- hard-particle indentation of raceways in unfiltered oil or open arrangements
- fretting corrosion on a loose rotating shaft seat
Selection pitfalls — read before you substitute
- On this 40 mm bore, shaft thermal growth can preload the inner ring if the fit is too tight; verify residual interference at temperature and confirm the float ring still slides after mounting NN3008K.
- The EA high-capacity roller complement changes the load figure versus the basic execution of the same number; the 48/55.5 kN pair here belongs to NN3008K as printed, not to the bare size.
- Minimum radial load is frequently missed in oversized motor and fan selections: an underloaded NN3008K skids at 9,700 r/min and fails by smearing long before L10 fatigue.
- Never press either ring through the roller complement when fitting: mounting force goes through the ring faces, or the 68 mm race brinells and releases as vibration within hours.
- The NN rib arrangement is not interchangeable with another prefix on the same 40 mm seat: double row, ribbed inner ring, separable outer. Swapping NU for NJ changes axial location behaviour even though the 68×21 mm envelope matches.
- The 48/55.5 kN ratings, 6.75 kN Pu and 303 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NN3008K (standard execution); other makes sharing the ISO 15 envelope revise internal geometry without changing the order number, so keep the 2203E reference with the specification for critical drives.
Frequently asked questions
What are the dimensions and catalogue data of NN3008K?
NN3008K is an NTN NN double-row precision cylindrical roller bearing to ISO 15: 40 mm bore, 68 mm OD and 21 mm width (1.575 × 2.677 × 0.827 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 48 kN, C0 55.5 kN, Pu 6.75 kN, grease limiting speed 9,700 r/min, oil 11,000 r/min, mass about 303 g. It is open, with a machined or stamped steel cage per the precision execution.
What is the difference between NU, NJ, NUP, N and NF cylindrical roller bearings?
NN and NNU are double-row precision designs rather than single-row rib variants: NN has a ribbed inner ring and separable outer ring, NNU the reverse; both give high radial stiffness for spindles and are commonly ordered with P5/P4 precision and a K 1:12 tapered bore for preload setting. NN3008K is the NN execution.
What do the EA, E and ＊ suffixes mean on NTN cylindrical roller bearings?
EA is NTN's high-capacity design with a pressed sheet-steel cage and optimised roller complement in the same ISO 15 envelope; E marks the high-capacity design at the larger bores; the ＊ symbol printed before the code in the NTN catalogue marks the ULTAGE new-generation specification and is not typed as part of the order number. NN3008K is supplied in the standard open execution shown in the table.
What does the K tapered bore mean on a precision NN bearing like NN3008K?
The K suffix denotes a 1:12 tapered bore. NN3008K mounts on a tapered shaft seat or adapter sleeve and is driven up to a measured residual clearance or preload — this is how precision spindle bearings achieve stiffness without locknut guesswork; the cylindrical-bore NN3008 execution of the same envelope mounts on a plain seat.
What speeds and lubrication apply to NN3008K?
NTN rates NN3008K at 9,700 r/min with grease and 11,000 r/min with oil. The grease figure is the cage/film mechanical ceiling; the oil figure assumes circulating or carefully supplied oil that removes heat from the line-contact zone.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN Ball and Roller Bearings CAT.No.2203E on 2026-10-01. Read our editorial & correction policy.