NNU4944K bearing: complete specifications & equivalents
The NNU4944K is a ISO 15 radial bearing sized 220 x 300 x 80 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 220 mm |
| Outer diameter D | 300 mm |
| Width B | 80 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 650 kN |
| Basic static load rating C0 | 1300 kN |
| Fatigue load limit Pu | 118 kN |
| Limiting speed (mechanical) | 1900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 15200 g |
| Manufacturer designation | NTN NNU4944K |
| 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 & NNU4900-series range
| Bore d | 8.661 in |
|---|---|
| Outer diameter D | 11.811 in |
| Width B | 3.15 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 40 mm |
| Smallest bore in NNU4900-series | 100 mm |
| Largest outer diameter in NNU4900-series | 650 mm |
| Width range across NNU4900-series | 40–170 mm |
| Bore position in NNU4900-series (smallest first) | 13 of 26 |
| Bore above smallest NNU4900-series size | 120 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NNU4944K | 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 NNU4944K model number is decoded
For pure radial duty on a 220 mm shaft NTN supplies NNU4944K: two integral ribs on the outer ring and a ribless, separable inner ring; the open execution is rated 1,900 r/min on grease and 2,200 r/min on oil. On the NTN nameplate NNU states which ring carries the ribs, which determines whether NNU4944K floats or locates; the numeric remainder is the ISO 15 series and 220 mm bore reference, not a fit or clearance instruction. At 2,200 r/min with oil versus 1,900 r/min with grease (a 300 r/min band), lubrication choice for NNU4944K is a thermal decision, not just a sealing one. Mass 15200 g for the 220×300×80 mm NNU4944K execution covers the pressed-steel cage and full roller complement; substitute on mass plus rating, not envelope alone. Heat the inner ring to max 120 °C for the 220 mm interference fit and support the ring face square during fitting; cocking over a keyway brinells the raceway before first rotation.
Typical equipment & failure modes
Common applications
- precision rotary-table and dividing-head bearings
- high-speed turbine and turbo-blower rotor supports
- coordinate-measuring and semiconductor-equipment drives
- machine-tool main spindles requiring high radial stiffness
Known failure patterns
- inner-ring raceway spalling from overload in the line-contact Hertzian zone
- pressed-steel cage pocket wear when rollers skid at light load or too-thin lubricant
- grease starvation and cage drag when relubrication intervals are extended past the grease life
- brinelling from static overload or impact during handling
- edge loading from shaft deflection beyond the 3–4 arc-minute alignment limit
Selection pitfalls — read before you substitute
- At 220 mm bore, oil-lubricated arrangements toward 2,200 r/min need positive flow and drain design; the 15200 g NNU4944K ring stores enough heat that grease-only duty needs a careful relubrication calculation.
- Grease limiting speed 1,900 r/min and oil 2,200 r/min are different limits for NNU4944K: the first is the cage/lubricant mechanical ceiling, the second assumes real oil flow rather than an oil bath.
- The 40.0 mm section at 220 mm bore leaves a narrow oil path; with the standard cage the relubrication groove and oil-level design must keep grease from churning in the 80 mm-wide cavity.
- The K tapered bore of NNU4944K is driven up to a measured clearance: skipping the drive-up procedure in favour of a normal press fit leaves the precision spindle set either preloaded hot or loose under load.
- Grease limiting speed 1,900 r/min and oil 2,200 r/min are different limits for NNU4944K: the first is the cage/lubricant mechanical ceiling, the second assumes real oil flow rather than an oil bath.
- The 650/1300 kN ratings, 118 kN Pu and 15200 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NNU4944K (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 NNU4944K?
NNU4944K is an NTN NNU double-row precision cylindrical roller bearing to ISO 15: 220 mm bore, 300 mm OD and 80 mm width (8.661 × 11.811 × 3.15 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 650 kN, C0 1300 kN, Pu 118 kN, grease limiting speed 1,900 r/min, oil 2,200 r/min, mass about 15200 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. NNU4944K is the NNU 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. NNU4944K is supplied in the standard open execution shown in the table.
What does the K tapered bore mean on a precision NNU bearing like NNU4944K?
The K suffix denotes a 1:12 tapered bore. NNU4944K 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 NNU4944 execution of the same envelope mounts on a plain seat.
What do Fw and Ew mean for NNU4944K?
Fw is the inner sub-assembly raceway/roller-set envelope diameter and Ew the outer-ring raceway diameter printed for geometric checks: Fw 245 mm. The nominal bore/OD remain 220/300 mm; Fw/Ew describe the rolling-contact path, and speeds still run to 1,900 r/min grease / 2,200 r/min oil.
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.