A4050-A4138 bearing: complete specifications & equivalents
The A4050-A4138 is a ANSI ABMA 19.2 radial bearing sized 12.7 x 34.988 x 10.998 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 12.7 mm |
| Outer diameter D | 34.988 mm |
| Width B | 10.998 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 13.7 kN |
| Basic static load rating C0 | 11.6 kN |
| Limiting speed (mechanical) | 12000 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 53 g |
| Manufacturer designation | NTN 4T-A4050/A4138 |
| 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 | 0.5 in |
|---|---|
| Outer diameter D | 1.377 in |
| Width B | 0.433 in |
| ISO bore code | 50 |
| Radial section height (D−d)/2 | 11.1 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) | 1 of 148 |
| Bore above smallest 4t-inch-series size | 0 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| A4050 | 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 A4050-A4138 model number is decoded
In NTN Ball and Roller Bearings CAT.No.2203E, the order number 4T-A4050/A4138 denotes the A small-size family of NTN inch tapered roller bearings — cone A4050 and cup A4138 delivered as a matched, separable pair of 12.7 mm bore and 34.988 mm outside diameter. Letter prefixes inherited from the inch convention mark the load family: LM reads as light-medium, HM as heavy-medium, LL as extra-light, J-prefixed codes as metric-envelope families — A4050 sits in the A small-size family. The 1.1 kN of dynamic capacity per millimetre of bore summarises the 13.7 kN rating over the 12.7 mm bore — sanity-check any interchange candidate against this ratio and the 10.998 mm T. Cup-side note for A4138: within the A small-size family tables the A4050 cone is listed against several cup options, and it is the cup that fixes the 34.988 mm OD and the 10.998 mm assembled width — quote the full A4050/A4138 pair, never the cone alone. The rollers run with their large ends against the cone's guide rib; lubricant must reach that rib face of 4T-A4050/A4138, not only the raceway, or the pair smears on the first overloaded start.
Typical equipment & failure modes
Common applications
- small agricultural implement wheels and auger drives
- lawn, garden and powersport axle positions
- small inch-shaft gearbox and reducer shafts
- conveyor roller and pulley shafts in inch-frame machinery
Known failure patterns
- cone-rib and roller large-end smearing when the adjusted pair runs with preload but starved lubricant film
- preload loss and noise after one bearing of the adjusted pair is replaced without resetting end play
- false brinelling on a stationary pair exposed to vibration during transport or standby
- cage fatigue when the pair runs continuously near the grease limiting speed without oil cooling
- rolling-contact fatigue spalling after the catalogue L10 life at the actual combined load
Selection pitfalls — read before you substitute
- At 12.7 mm (0.5 in) bore the thin cone and cup distort under an over-tight shaft nut; set the 4T-A4050/A4138 pair with a dial indicator on end play rather than by locknut feel.
- The A small-size family at 12.7 mm bore (34.988×10.998 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full A4050/A4138 reference at purchase.
- Never drive the 34.988 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.
- Shaft and housing fillets must clear the ring chamfers of A4050 and A4138; use undercut shoulders so the rings seat on the face, not on a radius.
- Quote the full A4050/A4138 pair at ordering: the A4050 cone also ships against sibling cups, and a cup from another reference changes the 10.998 mm assembled width and the rating.
- The 13.7/11.6 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-A4050/A4138; 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-A4050/A4138?
4T-A4050/A4138 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 12.7 mm bore (0.5 in), 34.988 mm outside diameter and 10.998 mm assembled width T (1.377 × 0.433 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 13.7 kN, C0 11.6 kN, grease limiting speed 12,000 r/min, oil speed 16,000 r/min, mass about 53 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-A4050/A4138 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the A4050 cone or the A4138 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 13.7/11.6 kN ratings change with the cup.
What is the difference between 4T-A4050/A4138 and a metric ISO 355 tapered bearing?
4T-A4050/A4138 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 12.7×34.988×10.998 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-A4050/A4138 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 A4050/A4138 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-A4050/A4138 list two speeds, 12,000 and 16,000 r/min?
The lower figure, 12,000 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-A4050/A4138 at 16,000 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.