34300-34478 bearing: complete specifications & equivalents
The 34300-34478 is a ANSI ABMA 19.2 radial bearing sized 76.2 x 121.442 x 24.608 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 76.2 mm |
| Outer diameter D | 121.442 mm |
| Width B | 24.608 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 101 kN |
| Basic static load rating C0 | 127 kN |
| Limiting speed (mechanical) | 2900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 978 g |
| Manufacturer designation | NTN 4T-34300/34478 |
| 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 | 3 in |
|---|---|
| Outer diameter D | 4.781 in |
| Width B | 0.969 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 22.6 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) | 94 of 148 |
| Bore above smallest 4t-inch-series size | 63.5 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 34300 | 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 34300-34478 model number is decoded
For an inch shaft of 76.2 mm carrying combined radial and thrust load, NTN lists 4T-34300/34478, a single-row 4T tapered roller set of 101 kN C and 127 kN C0 inside the 121.442 mm OD cup. 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 34300/34478 without it. Selection: C 101 kN against C0 127 kN gives a C0/C ratio of 1.26 for the 76.2 mm bore; the pair is counted as one adjusted unit when checking L10 at the equivalent combined load. Housing fitment sequence for 4T-34300/34478: press the 34478 cup square into the 121.442 mm seat first, then bring the 34300 cone (on its 76.2 mm shaft) into adjustment — the two references are separate engineering parts that happen to ship as one set. Fillet radii must clear the chamfers of the 34300 cone and 34478 cup; undercut shoulders seat the rings fully instead of bridging on a radius.
Typical equipment & failure modes
Common applications
- plant gearboxes on inch-dimensioned shaft lines
- large conveyor head pulleys in bulk-handling plant
- paper-machine and calender roll supports
- off-highway and forestry machine axles
Known failure patterns
- cone-rib and roller large-end smearing when the adjusted pair runs with preload but starved lubricant film
- flaking on one cone only when a bent shaft loads the O/X pair unevenly
- cup creep and housing fretting when the cup seat is cut too loose for the rotating load
- cage fatigue when the pair runs continuously near the grease limiting speed without oil cooling
- edge loading when shaft deflection exceeds the few arc-minutes an adjusted pair tolerates
Selection pitfalls — read before you substitute
- Mount the 76.2 mm cone by induction heating (max 120 °C) and the 121.442 mm cup with a press sleeve; at 978 g a cocked ring brinells the raceway directly.
- The pure-numeric inch family at 76.2 mm bore (121.442×24.608 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 34300/34478 reference at purchase.
- Never drive the 121.442 mm cup home through the rollers: fitting force goes through the ring faces only, or brinell marks release as noise within the first running hours.
- Do not confuse T (24.608 mm, the assembled cone-plus-cup width) with the cone width when drawing spacers; an abutment sized to T leaves the cup unseated.
- Fit selection follows the rotating ring: a rotating cone on a 76.2 mm shaft takes a k5/m5 seat, and a rotating cup reverses the logic — decide from the load diagram, not from habit.
- The 101/127 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-34300/34478; 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-34300/34478?
4T-34300/34478 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 76.2 mm bore (3 in), 121.442 mm outside diameter and 24.608 mm assembled width T (4.781 × 0.969 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 101 kN, C0 127 kN, grease limiting speed 2,900 r/min, oil speed 3,800 r/min, mass about 978 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-34300/34478 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 34300 cone or the 34478 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 101/127 kN ratings change with the cup.
What is the difference between 4T-34300/34478 and a metric ISO 355 tapered bearing?
4T-34300/34478 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 76.2×121.442×24.608 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-34300/34478 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 34300/34478 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-34300/34478 list two speeds, 2,900 and 3,800 r/min?
The lower figure, 2,900 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-34300/34478 at 3,800 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.