3478-3420 bearing: complete specifications & equivalents
The 3478-3420 is a ANSI ABMA 19.2 radial bearing sized 34.925 x 79.375 x 29.37 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 34.925 mm |
| Outer diameter D | 79.375 mm |
| Width B | 29.37 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 103 kN |
| Basic static load rating C0 | 114 kN |
| Limiting speed (mechanical) | 4900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 731 g |
| Manufacturer designation | NTN 4T-3478/3420 |
| 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 | 1.375 in |
|---|---|
| Outer diameter D | 3.125 in |
| Width B | 1.156 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 22.2 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) | 34 of 148 |
| Bore above smallest 4t-inch-series size | 22.224999999999998 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 3478 | 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 3478-3420 model number is decoded
4T-3478/3420 is an NTN inch-series single-row tapered roller bearing: a separable cone-and-cup pair on the ABMA inch boundary plan, 34.925×79.375×29.37 mm (assembled width T), for a shaft of about 34.925 mm (1.375 in). The 4T prefix is NTN's tapered roller quality mark stamped on both parts; it is a brand mark, not a size code, so cross-references quote 3478/3420 without it. Contact-angle geometry of the pure-numeric inch family gives 4T-3478/3420 its radial/axial load split — at 103/114 kN the static rating is about 1.11× C, typical of inch tapered sets proportioned for combined duty. The printed 103/114 kN ratings belong to the assembled 3478+3420 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. With a rotating shaft a k5/m5 cone seat and an easy-push cup seat are typical practice for 4T-3478/3420; reverse the fit logic when the cup rotates.
Typical equipment & failure modes
Common applications
- construction-equipment pivot and wheel positions
- mining and quarry conveyor drive pulleys
- machine-tool headstocks on inch spindles
- pump and blower drive shafts with combined load
Known failure patterns
- rib-face scoring when the thrust share of the combined load exceeds what the cone rib of this size carries
- false brinelling on a stationary pair exposed to vibration during transport or standby
- preload loss and noise after one bearing of the adjusted pair is replaced without resetting end play
- cage fatigue when the pair runs continuously near the grease limiting speed without oil cooling
- indentation of the raceways by hard particles in an open, unsealed arrangement
Selection pitfalls — read before you substitute
- Hub and pinion positions of this 34.925 mm class are adjusted in pairs; verify end play against the axle or gearbox drawing and re-torque after bedding-in instead of trusting the first setting on 4T-3478/3420.
- The pure-numeric inch family at 34.925 mm bore (79.375×29.37 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 3478/3420 reference at purchase.
- Fit selection follows the rotating ring: a rotating cone on a 34.925 mm shaft takes a k5/m5 seat, and a rotating cup reverses the logic — decide from the load diagram, not from habit.
- Do not confuse T (29.37 mm, the assembled cone-plus-cup width) with the cone width when drawing spacers; an abutment sized to T leaves the cup unseated.
- Open 4T-3478/3420 sets have no seals: a hub or gearbox needs external sealing or the 4,900 r/min grease figure is meaningless once water reaches the cone rib.
- The 103/114 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-3478/3420; 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-3478/3420?
4T-3478/3420 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 34.925 mm bore (1.375 in), 79.375 mm outside diameter and 29.37 mm assembled width T (3.125 × 1.156 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 103 kN, C0 114 kN, grease limiting speed 4,900 r/min, oil speed 6,600 r/min, mass about 731 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-3478/3420 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 3478 cone or the 3420 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 103/114 kN ratings change with the cup.
What is the difference between 4T-3478/3420 and a metric ISO 355 tapered bearing?
4T-3478/3420 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 34.925×79.375×29.37 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-3478/3420 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 3478/3420 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-3478/3420 list two speeds, 4,900 and 6,600 r/min?
The lower figure, 4,900 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-3478/3420 at 6,600 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.