2879-2820 bearing: complete specifications & equivalents
The 2879-2820 is a ANSI ABMA 19.2 radial bearing sized 31.75 x 73.025 x 22.225 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 31.75 mm |
| Outer diameter D | 73.025 mm |
| Width B | 22.225 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 69.5 kN |
| Basic static load rating C0 | 75.5 kN |
| Limiting speed (mechanical) | 5200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 466 g |
| Manufacturer designation | NTN 4T-2879/2820 |
| 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 | 1.25 in |
|---|---|
| Outer diameter D | 2.875 in |
| Width B | 0.875 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 20.6 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) | 32 of 148 |
| Bore above smallest 4t-inch-series size | 19.05 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 2879 | 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 2879-2820 model number is decoded
NTN supplies this 1.25 in (31.75 mm) shaft position as 4T-2879/2820: cone 2879, cup 2820, profiled rollers and a pressed-steel cage, rated 69.5 kN basic dynamic and 75.5 kN static. Cone and cup of 4T-2879/2820 are separately stocked parts: a worn 2820 cup can be replaced against the existing 2879 cone, provided the new cup carries the identical reference — pairing across references changes the 22.225 mm assembled width and the rating. The 20.6 mm radial section over the 31.75 mm bore positions the contact line of the pair; abutment shoulders and spacers are dimensioned from that geometry, not from the bore alone. The printed 69.5/75.5 kN ratings belong to the assembled 2879+2820 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-2879/2820 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
- industrial gearboxes built to inch shafting
- construction-equipment pivot and wheel positions
- mining and quarry conveyor drive pulleys
- machine-tool headstocks on inch spindles
Known failure patterns
- rib-face scoring when the thrust share of the combined load exceeds what the cone rib of this size carries
- 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
- 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 31.75 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-2879/2820.
- The pure-numeric inch family at 31.75 mm bore (73.025×22.225 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 2879/2820 reference at purchase.
- Fit selection follows the rotating ring: a rotating cone on a 31.75 mm shaft takes a k5/m5 seat, and a rotating cup reverses the logic — decide from the load diagram, not from habit.
- Open 4T-2879/2820 sets have no seals: a hub or gearbox needs external sealing or the 5,200 r/min grease figure is meaningless once water reaches the cone rib.
- ABMA makes the 31.75×73.025 mm envelope interchangeable, not the ratings: NTN prints 69.5/75.5 kN for this execution and another make of the same number can differ in roller complement.
- The 69.5/75.5 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-2879/2820; 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-2879/2820?
4T-2879/2820 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 31.75 mm bore (1.25 in), 73.025 mm outside diameter and 22.225 mm assembled width T (2.875 × 0.875 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 69.5 kN, C0 75.5 kN, grease limiting speed 5,200 r/min, oil speed 7,000 r/min, mass about 466 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-2879/2820 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 2879 cone or the 2820 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 69.5/75.5 kN ratings change with the cup.
What is the difference between 4T-2879/2820 and a metric ISO 355 tapered bearing?
4T-2879/2820 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 31.75×73.025×22.225 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-2879/2820 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 2879/2820 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-2879/2820 list two speeds, 5,200 and 7,000 r/min?
The lower figure, 5,200 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-2879/2820 at 7,000 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.