LM78349A-LM78310A bearing: complete specifications & equivalents
The LM78349A-LM78310A is a ANSI ABMA 19.2 radial bearing sized 34.988 x 61.973 x 16.7 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 34.988 mm |
| Outer diameter D | 61.973 mm |
| Width B | 16.7 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 41 kN |
| Basic static load rating C0 | 48 kN |
| Limiting speed (mechanical) | 5900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 206 g |
| Manufacturer designation | NTN 4T-LM78349A/LM78310A |
| 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 | 1.377 in |
|---|---|
| Outer diameter D | 2.44 in |
| Width B | 0.657 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 13.5 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) | 36 of 148 |
| Bore above smallest 4t-inch-series size | 22.288 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| LM78349A | 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 LM78349A-LM78310A model number is decoded
4T-LM78349A/LM78310A is an NTN inch-series single-row tapered roller bearing: a separable cone-and-cup pair on the ABMA inch boundary plan, 34.988×61.973×16.7 mm (assembled width T), for a shaft of about 34.988 mm (1.377 in). Reading the designation: 4T-LM78349A/LM78310A follows the ABMA inch convention — the number before the slash is the cone (inner ring with roller set and cage), the number after the slash is the cup (outer ring), and the light-medium LM family lettering ties the pair to its boundary plan. Selection: C 41 kN against C0 48 kN gives a C0/C ratio of 1.17 for the 34.988 mm bore; the pair is counted as one adjusted unit when checking L10 at the equivalent combined load. The printed 41/48 kN ratings belong to the assembled LM78349A+LM78310A 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. Running clearance of 4T-LM78349A/LM78310A is set at mounting by axial displacement of cone or cup — the catalogue does not ship a preloaded set, so the drawing must state end play or preload.
Typical equipment & failure modes
Common applications
- mining and quarry conveyor drive pulleys
- machine-tool headstocks on inch spindles
- pump and blower drive shafts with combined load
- truck and trailer axle hubs on inch-dimensioned axles
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
- pressed-steel cage pocket wear from roller skid at light radial load and high speed
- indentation of the raceways by hard particles in an open, unsealed arrangement
Selection pitfalls — read before you substitute
- Hub and pinion positions of this 34.988 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-LM78349A/LM78310A.
- The light-medium LM family at 34.988 mm bore (61.973×16.7 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full LM78349A/LM78310A reference at purchase.
- Do not confuse T (16.7 mm, the assembled cone-plus-cup width) with the cone width when drawing spacers; an abutment sized to T leaves the cup unseated.
- Never drive the 61.973 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.
- Never drive the 61.973 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.
- The 41/48 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-LM78349A/LM78310A; 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-LM78349A/LM78310A?
4T-LM78349A/LM78310A is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 34.988 mm bore (1.377 in), 61.973 mm outside diameter and 16.7 mm assembled width T (2.44 × 0.657 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 41 kN, C0 48 kN, grease limiting speed 5,900 r/min, oil speed 7,900 r/min, mass about 206 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-LM78349A/LM78310A interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the LM78349A cone or the LM78310A 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 41/48 kN ratings change with the cup.
What is the difference between 4T-LM78349A/LM78310A and a metric ISO 355 tapered bearing?
4T-LM78349A/LM78310A 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 34.988×61.973×16.7 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-LM78349A/LM78310A 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 LM78349A/LM78310A references; the 4T spelling is retained among this page's search aliases.
Why does 4T-LM78349A/LM78310A list two speeds, 5,900 and 7,900 r/min?
The lower figure, 5,900 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-LM78349A/LM78310A at 7,900 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.