621-612 bearing: complete specifications & equivalents
The 621-612 is a ANSI ABMA 19.2 radial bearing sized 53.975 x 120.65 x 41.275 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 53.975 mm |
| Outer diameter D | 120.65 mm |
| Width B | 41.275 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 190 kN |
| Basic static load rating C0 | 213 kN |
| Limiting speed (mechanical) | 3300 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 2220 g |
| Manufacturer designation | NTN 4T-621/612 |
| 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 | 2.125 in |
|---|---|
| Outer diameter D | 4.75 in |
| Width B | 1.625 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 33.3 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) | 67 of 148 |
| Bore above smallest 4t-inch-series size | 41.275000000000006 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 621 | 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 621-612 model number is decoded
4T-621/612 is the NTN 4T catalogue entry for a 53.975×120.65×41.275 mm inch tapered roller bearing — an ABMA-dimensioned cone/cup set, not an ISO 355 metric bearing, even though the table quotes metric equivalents. Reading the designation: 4T-621/612 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 pure-numeric inch family lettering ties the pair to its boundary plan. Catalogue mass of the 4T-621/612 cone-plus-cup set is 2220 g; shaft and housing shoulders must carry that mass square to the axis during fitting. Cup-side note for 612: within the pure-numeric inch family tables the 621 cone is listed against several cup options, and it is the cup that fixes the 120.65 mm OD and the 41.275 mm assembled width — quote the full 621/612 pair, never the cone alone. After bedding-in, re-check the end play of the adjusted 4T-621/612 pair — initial seating of the ring faces relaxes the setting slightly.
Typical equipment & failure modes
Common applications
- agricultural tractor transmission and PTO shafts
- industrial gearboxes built to inch shafting
- construction-equipment pivot and wheel positions
- mining and quarry conveyor drive pulleys
Known failure patterns
- rib-face scoring when the thrust share of the combined load exceeds what the cone rib of this size carries
- 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
- pressed-steel cage pocket wear from roller skid at light radial load and high speed
- rolling-contact fatigue spalling after the catalogue L10 life at the actual combined load
Selection pitfalls — read before you substitute
- Hub and pinion positions of this 53.975 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-621/612.
- The pure-numeric inch family at 53.975 mm bore (120.65×41.275 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 621/612 reference at purchase.
- ABMA makes the 53.975×120.65 mm envelope interchangeable, not the ratings: NTN prints 190/213 kN for this execution and another make of the same number can differ in roller complement.
- Inch and metric bores collide on paper — 53.975 mm is 2.125 in, not a round metric size; a metric bearing that seems 0.1 mm off will not seat on the inch shaft.
- Replacing one half of an adjusted pair without resetting end play negates the 41.275 mm T logic: re-adjust the set and re-verify the contact pattern rather than reusing the old spacer stack.
- The 190/213 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-621/612; 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-621/612?
4T-621/612 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 53.975 mm bore (2.125 in), 120.65 mm outside diameter and 41.275 mm assembled width T (4.75 × 1.625 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 190 kN, C0 213 kN, grease limiting speed 3,300 r/min, oil speed 4,400 r/min, mass about 2220 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-621/612 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 621 cone or the 612 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 190/213 kN ratings change with the cup.
What is the difference between 4T-621/612 and a metric ISO 355 tapered bearing?
4T-621/612 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 53.975×120.65×41.275 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-621/612 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 621/612 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-621/612 list two speeds, 3,300 and 4,400 r/min?
The lower figure, 3,300 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-621/612 at 4,400 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.