7938 bearing: complete specifications & equivalents
The 7938 is a ISO 15 radial bearing sized 190 x 260 x 33 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 | 33 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | brass |
| Basic dynamic load rating C | 147 kN |
| Basic static load rating C0 | 169 kN |
| Fatigue load limit Pu | 7.45 kN |
| Limiting speed (mechanical) | 2400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 5100 g |
| Manufacturer designation | NTN 7938 |
| 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 & 7900-series range
| Bore d | 7.48 in |
|---|---|
| Outer diameter D | 10.236 in |
| Width B | 1.299 in |
| ISO bore code | 38 |
| Radial section height (D−d)/2 | 35 mm |
| Smallest bore in 7900-series | 25 mm |
| Largest outer diameter in 7900-series | 420 mm |
| Width range across 7900-series | 9–56 mm |
| Bore position in 7900-series (smallest first) | 26 of 32 |
| Bore above smallest 7900-series size | 165 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 7938 | 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. |
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 7938 model number is decoded
NTN 7938 belongs to the extra-light, high-speed 7900 single-row family: the catalogue boundary dimensions read 190 / 260 / 33 mm (bore / OD / width). The designation breaks down as 79 is the single-row dimension series (extra-light, high-speed 7900 single-row family); 38 encodes the 190 mm bore (bore code x 5); with no letter after the digits it is the standard 30 deg contact-angle execution — the 40 deg version carries a B. Catalogue mass is about 5100 g, which at this 35.0 mm radial section keeps the bearing comfortably inside high-speed spindle weight budgets. Selection starts from the thrust share: as axial load grows past roughly half the radial load, an angular-contact position of this section usually outlives a deep-groove one. Grease quantity matters as much as grade at 2,400 r/min: fill about a third of the free space and let the bearing purge on first run.
Typical equipment & failure modes
Common applications
- large pump and turbine auxiliary shafts
- steel-plant conveyor and table roll drives
- wind-turbine and heavy-machinery auxiliaries
- heavy industrial gearbox main shafts
Known failure patterns
- false brinelling on the raceway contact ellipses when a preloaded spindle sits vibrating at standstill — visible as evenly spaced flute-like wear at ball pitch
- thermal runaway from excessive preload: the pair runs hot, grease darkens and the contact ellipse spreads until the raceways smear
- machined-cage land scoring when a high-speed spindle runs past its grease rating and the cage runs dry on its guidance surface
- contamination-induced denting — hard particles rolled into the contact ellipse become the initiation points for surface fatigue
- lubricant starvation scoring at the ball/raceway contact when grease volume or relubrication interval is guessed instead of calculated
Selection pitfalls — read before you substitute
- At this size the shaft fit, shoulder geometry and preload procedure dominate the outcome; a 190 mm bore bearing forgives nothing in a poorly machined housing.
- The 7900 extra-light section is chosen for speed and stiffness, not for load margin — check that C0 169 kN really covers the worst static case before substituting it for a 7000.
- A 7938 mounted the wrong way round still turns smoothly by hand; the failure shows up weeks later as raceway flaking on the unloaded-looking side.
- Substituting the B (40 deg) execution for the standard 30 deg bearing changes the axial/radial load split — the shaft position and the mating bearing see different forces even though the envelope is identical.
- If the application vibrates at standstill (transport, idle machine next to a running line), specify protection: the contact ellipse of a preloaded bearing false-brinells faster than a loose one.
- The 147/169 kN ratings and 7.45 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 7938; internal geometry legitimately differs between manufacturers, so re-verify ratings, contact angle and suffix before substituting another make on a rated drive.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 7938?
7938 is a single-row angular contact ball bearing to ISO 15: 190 mm bore, 260 mm outside diameter, 33 mm width (7.48 x 10.236 x 1.299 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 147 kN, C0 169 kN and a 7.45 kN fatigue load limit Pu; the grease limiting speed is 2,400 r/min and the oil rating 3,200 r/min; mass about 5100 g.
How is the 7938 designation structured?
79 is the single-row dimension series (extra-light, high-speed 7900 single-row family); 38 encodes the 190 mm bore (bore code x 5); with no letter after the digits it is the standard 30 deg contact-angle execution — the 40 deg version carries a B. The 260 mm OD and 33 mm width follow the ISO 15 boundary-dimension plan for that series.
Which axial direction does 7938 support?
One 7938 alone takes thrust in one direction only, along its 30 deg contact angle; reversing thrust calls for a second bearing or a factory-matched DB/DF/DT pair (the catalogue right-hand columns list the paired ratings). Radial load is always carried as a combined load through the angled contact.
What lubrication speeds does NTN print for 7938?
Per NTN Ball and Roller Bearings CAT.No.2203E, the grease limiting speed is 2,400 r/min and the oil rating 3,200 r/min. These are catalogue ceilings for a correctly mounted bearing with the stated lubricant; preload, fill quantity, ambient heat and paired arrangements all move the real limit.
What should be checked before substituting another make for 7938?
The 190/260/33 mm envelope is ISO 15 interchangeable, but internal geometry — contact angle, osculation, cage and shoulder details — is maker-specific. Re-verify C 147 kN / C0 169 kN, the speed figures, contact angle and suffix meaning against the donor catalogue before swapping on a rated drive.
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.