NNU4988K bearing: complete specifications & equivalents
The NNU4988K is a ISO 15 radial bearing sized 440 x 600 x 160 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 440 mm |
| Outer diameter D | 600 mm |
| Width B | 160 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 2380 kN |
| Basic static load rating C0 | 5550 kN |
| Fatigue load limit Pu | 410 kN |
| Limiting speed (mechanical) | 850 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 121000 g |
| Manufacturer designation | NTN NNU4988K |
| 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 | 17.323 in |
|---|---|
| Outer diameter D | 23.622 in |
| Width B | 6.299 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 80 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) | 24 of 26 |
| Bore above smallest NNU4900-series size | 340 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NNU4988K | 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 NNU4988K model number is decoded
The NTN order number NNU4988K denotes a 440×600×160 mm (17.323 × 23.622 × 6.299 in) cylindrical roller bearing in the NNU4900 family, a machined or stamped steel cage per the precision execution. Reading the code: NNU for the double-row precision type, then the ISO 15 diameter/width series and the bore code — ×5 = 440 mm (00–03 use the 10/12/15/17 exception table). Line contact between rollers and raceways gives NNU4988K high radial capacity but no tolerance for misalignment: beyond roughly 3–4 arc-minutes the roller ends edge-load and fatigue accelerates. Thermal planning around the 850 r/min grease ceiling should include the cage type (a machined or stamped steel cage per the precision execution) and oil-flow option to 1,000 r/min for continuously high-duty 440 mm positions. On NNU 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
- precision gearbox and indexing-drive shafts
- high-rpm motorised grinding and milling spindles
- CNC lathe and machining-centre spindle radial sets
- precision rotary-table and dividing-head bearings
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
- electrical pitting on VFD-driven motor shafts without grounding protection
- edge loading from shaft deflection beyond the 3–4 arc-minute alignment limit
Selection pitfalls — read before you substitute
- At 440 mm bore, oil-lubricated arrangements toward 1,000 r/min need positive flow and drain design; the 121000 g NNU4988K ring stores enough heat that grease-only duty needs a careful relubrication calculation.
- The 160 mm width and abutment faces must be square to the axis; a tilted spacer concentrates load across the roller set and shows as uneven raceway polish on the 440 mm inner ring.
- The NNU rib arrangement is not interchangeable with another prefix on the same 440 mm seat: double row, ribbed outer ring, separable inner. Swapping NU for NJ changes axial location behaviour even though the 600×160 mm envelope matches.
- The NNU rib arrangement is not interchangeable with another prefix on the same 440 mm seat: double row, ribbed outer ring, separable inner. Swapping NU for NJ changes axial location behaviour even though the 600×160 mm envelope matches.
- Wide (22/23) and light (10/49) executions at 440 mm bore share bore but not OD/width; check the full NNU4900 series code before substituting, because housing and shoulder geometry will not interchange.
- The 2380/5550 kN ratings, 410 kN Pu and 121000 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NNU4988K (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 NNU4988K?
NNU4988K is an NTN NNU double-row precision cylindrical roller bearing to ISO 15: 440 mm bore, 600 mm OD and 160 mm width (17.323 × 23.622 × 6.299 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 2380 kN, C0 5550 kN, Pu 410 kN, grease limiting speed 850 r/min, oil 1,000 r/min, mass about 121000 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. NNU4988K 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. NNU4988K is supplied in the standard open execution shown in the table.
What does the K tapered bore mean on a precision NNU bearing like NNU4988K?
The K suffix denotes a 1:12 tapered bore. NNU4988K 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 NNU4988 execution of the same envelope mounts on a plain seat.
What do Fw and Ew mean for NNU4988K?
Fw is the inner sub-assembly raceway/roller-set envelope diameter and Ew the outer-ring raceway diameter printed for geometric checks: Fw 492 mm. The nominal bore/OD remain 440/600 mm; Fw/Ew describe the rolling-contact path, and speeds still run to 850 r/min grease / 1,000 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.