NN4938K bearing: complete specifications & equivalents
The NN4938K is a ISO 15 radial bearing sized 190 x 260 x 69 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 190 mm |
| Outer diameter D | 260 mm |
| Width B | 69 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 525 kN |
| Basic static load rating C0 | 1030 kN |
| Fatigue load limit Pu | 98 kN |
| Limiting speed (mechanical) | 2200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 9470 g |
| Manufacturer designation | NTN NN4938K |
| 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 & NN4900-series range
| Bore d | 7.48 in |
|---|---|
| Outer diameter D | 10.236 in |
| Width B | 2.717 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 35 mm |
| Smallest bore in NN4900-series | 100 mm |
| Largest outer diameter in NN4900-series | 440 mm |
| Width range across NN4900-series | 40–118 mm |
| Bore position in NN4900-series (smallest first) | 11 of 18 |
| Bore above smallest NN4900-series size | 90 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| NN4938K | 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 NN4938K model number is decoded
NN4938K belongs to the NTN cylindrical roller range in NTN Ball and Roller Bearings CAT.No.2203E: line-contact rollers between ground raceways for a 525 kN dynamic rating in the 190 mm bore. Reading the code: NN for the double-row precision type, then the ISO 15 diameter/width series and the bore code — ×5 = 190 mm (00–03 use the 10/12/15/17 exception table). With C 525 kN and C0 1030 kN (C0/C ≈ 1.96) the bearing is proportioned for heavy radial load; the NU design carries no axial load and floats axially on both sides. With the inner ring rotating, catalogue practice is a m6/n6 shaft seat and an H7/H6 housing; the outer ring must remain free to creep slightly axially in non-locating NN arrangements. 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
- 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
- roller smearing (microwelding) at start-up before the oil film builds under insufficient radial load
- cage wear accelerated when the EA high-capacity roller complement runs continuously above its thermal balance
- micro-pitting when the EHL film falls below the composite roughness at high specific load
- rolling-contact fatigue after the catalogue L10 life is exceeded
- brinelling from static overload or impact during handling
Selection pitfalls — read before you substitute
- At 190 mm bore, oil-lubricated arrangements toward 2,600 r/min need positive flow and drain design; the 9470 g NN4938K ring stores enough heat that grease-only duty needs a careful relubrication calculation.
- Minimum radial load is frequently missed in oversized motor and fan selections: an underloaded NN4938K skids at 2,200 r/min and fails by smearing long before L10 fatigue.
- Open NN4938K units need application-supplied sealing and a defined lubricant schedule; film thickness is the first failure mode for line contact when viscosity drops at the 190 mm contact.
- Grease limiting speed 2,200 r/min and oil 2,600 r/min are different limits for NN4938K: the first is the cage/lubricant mechanical ceiling, the second assumes real oil flow rather than an oil bath.
- Minimum radial load is frequently missed in oversized motor and fan selections: an underloaded NN4938K skids at 2,200 r/min and fails by smearing long before L10 fatigue.
- The 525/1030 kN ratings, 98 kN Pu and 9470 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for NN4938K (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 NN4938K?
NN4938K is an NTN NN double-row precision cylindrical roller bearing to ISO 15: 190 mm bore, 260 mm OD and 69 mm width (7.48 × 10.236 × 2.717 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 525 kN, C0 1030 kN, Pu 98 kN, grease limiting speed 2,200 r/min, oil 2,600 r/min, mass about 9470 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. NN4938K 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. NN4938K is supplied in the standard open execution shown in the table.
What does the K tapered bore mean on a precision NN bearing like NN4938K?
The K suffix denotes a 1:12 tapered bore. NN4938K 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 NN4938 execution of the same envelope mounts on a plain seat.
What do Fw and Ew mean for NN4938K?
Fw is the inner sub-assembly raceway/roller-set envelope diameter and Ew the outer-ring raceway diameter printed for geometric checks: Fw 212 mm. The nominal bore/OD remain 190/260 mm; Fw/Ew describe the rolling-contact path, and speeds still run to 2,200 r/min grease / 2,600 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.