78250-78551 bearing: complete specifications & equivalents
The 78250-78551 is a ANSI ABMA 19.2 radial bearing sized 63.5 x 140.03 x 36.512 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 63.5 mm |
| Outer diameter D | 140.03 mm |
| Width B | 36.512 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 190 kN |
| Basic static load rating C0 | 212 kN |
| Limiting speed (mechanical) | 2600 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 2540 g |
| Manufacturer designation | NTN 4T-78250/78551 |
| Standard | ANSI ABMA 19.2 |
| Catalog version | NTN 2203E 2026-09-25 |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN 2203E 2026-09-25) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN 2203E 2026-09-25); 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 & 4t-inch-series range
| Bore d | 2.5 in |
|---|---|
| Outer diameter D | 5.513 in |
| Width B | 1.437 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 38.3 mm |
| Smallest bore in 4t-inch-series | 12.7 mm |
| Largest outer diameter in 4t-inch-series | 260 mm |
| Width range across 4t-inch-series | 10.998–77.788 mm |
| Bore position in 4t-inch-series (smallest first) | 81 of 148 |
| Bore above smallest 4t-inch-series size | 50.8 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 78250 | 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 78250-78551 model number is decoded
The NTN 2203E inch table prints 4T-78250/78551 at 63.5 mm bore (2.5 in), 140.03 mm cup OD and 36.512 mm assembled T, with a grease limiting speed of 2,600 r/min and an oil ceiling of 3,400 r/min. Cone and cup of 4T-78250/78551 are separately stocked parts: a worn 78551 cup can be replaced against the existing 78250 cone, provided the new cup carries the identical reference — pairing across references changes the 36.512 mm assembled width and the rating. Two single-row inch sets are normally mounted as an adjusted O or X pair; the 36.512 mm T of each 4T-78250/78551 enters the spacer calculation, so the tolerance on assembled width matters as much as the bore fit. The printed 190/212 kN ratings belong to the assembled 78250+78551 pair; a sibling row using the same cone with a different cup carries its own rating row because the raceway track shifts with the cup. NTN grades inch 4T bearings as open bearings without integral seals; at 63.5 mm bore the application supplies sealing and the grease fill or oil feed.
Typical equipment & failure modes
Common applications
- marine winch and deck-machinery shafts
- crusher and screening-plant eccentric shafts
- heavy truck and bus drive-axle differentials
- plant gearboxes on inch-dimensioned shaft lines
Known failure patterns
- cone-rib and roller large-end smearing when the adjusted pair runs with preload but starved lubricant film
- cup creep and housing fretting when the cup seat is cut too loose for the rotating load
- flaking on one cone only when a bent shaft loads the O/X pair unevenly
- cage damage from a mounting blow transmitted through the roller complement
- water-induced pitting when the open bearing sees washdown without external seals
Selection pitfalls — read before you substitute
- Mount the 63.5 mm cone by induction heating (max 120 °C) and the 140.03 mm cup with a press sleeve; at 2540 g a cocked ring brinells the raceway directly.
- The pure-numeric inch family at 63.5 mm bore (140.03×36.512 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 78250/78551 reference at purchase.
- ABMA makes the 63.5×140.03 mm envelope interchangeable, not the ratings: NTN prints 190/212 kN for this execution and another make of the same number can differ in roller complement.
- Grease packs must leave free volume inside the 36.512 mm-wide set; over-greasing a pair churning near the oil-band speed of 3,400 r/min raises temperature and destroys the setting.
- Open 4T-78250/78551 sets have no seals: a hub or gearbox needs external sealing or the 2,600 r/min grease figure is meaningless once water reaches the cone rib.
- The 190/212 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-78250/78551; internal geometry legitimately differs between inch-series makers, so re-verify ratings, adjustment and the exact cone/cup references before substituting another brand on a rated drive.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 4T-78250/78551?
4T-78250/78551 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 63.5 mm bore (2.5 in), 140.03 mm outside diameter and 36.512 mm assembled width T (5.513 × 1.437 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 190 kN, C0 212 kN, grease limiting speed 2,600 r/min, oil speed 3,400 r/min, mass about 2540 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-78250/78551 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 78250 cone or the 78551 cup can be replaced by an identical reference from NTN or another ABMA-dimensioned maker. Pairing the cone with a different cup reference is a different catalogue row: OD, assembled T and the 190/212 kN ratings change with the cup.
What is the difference between 4T-78250/78551 and a metric ISO 355 tapered bearing?
4T-78250/78551 follows the ABMA inch boundary plan with cone/cup references; ISO 355 bearings use metric dimension-series numbers (302, 322, …). Even where a metric size looks close to 63.5×140.03×36.512 mm, the envelopes and contact angles differ — the two systems are not drop-in interchangeable; check every boundary value before substituting.
What does the 4T prefix on 4T-78250/78551 mean?
4T is NTN's tapered roller bearing quality mark, stamped on cone and cup in the factory. It identifies NTN's 4T programme and is not a dimension or variant code, so interchange lists quote the bare 78250/78551 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-78250/78551 list two speeds, 2,600 and 3,400 r/min?
The lower figure, 2,600 r/min, is the grease-lubricated limiting speed — the mechanical ceiling for the cage, rollers and cone-rib contact. With oil lubrication NTN rates 4T-78250/78551 at 3,400 r/min because oil removes rib-contact heat better. Real limits still depend on pair adjustment, oil flow and cooling.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN 2203E 2026-09-25 on 2026-10-01. Read our editorial & correction policy.