3188-3120 bearing: complete specifications & equivalents
The 3188-3120 is a ANSI ABMA 19.2 radial bearing sized 31.75 x 72.626 x 30.162 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 | 72.626 mm |
| Width B | 30.162 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 93.5 kN |
| Basic static load rating C0 | 98 kN |
| Limiting speed (mechanical) | 5500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 606 g |
| Manufacturer designation | NTN 4T-3188/3120 |
| 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 | 2.859 in |
| Width B | 1.187 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 20.4 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 |
|---|---|---|---|
| 3188 | 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 3188-3120 model number is decoded
4T-3188/3120 is the NTN 4T catalogue entry for a 31.75×72.626×30.162 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-3188/3120 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. Imperial cross-check for the drawing: 31.75×72.626×30.162 mm converts to 1.25 × 2.859 × 1.187 in; the ABMA envelope swaps with like-numbered inch parts but the 93.5/98 kN ratings are NTN-specific. Housing fitment sequence for 4T-3188/3120: press the 3120 cup square into the 72.626 mm seat first, then bring the 3188 cone (on its 31.75 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 3188 cone and 3120 cup; undercut shoulders seat the rings fully instead of bridging on a radius.
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
- cone-rib and roller large-end smearing when the adjusted pair runs with preload but starved lubricant film
- false brinelling on a stationary pair exposed to vibration during transport or standby
- preload loss and noise after one bearing of the adjusted pair is replaced without resetting end play
- cage damage from a mounting blow transmitted through the roller complement
- edge loading when shaft deflection exceeds the few arc-minutes an adjusted pair tolerates
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-3188/3120.
- The pure-numeric inch family at 31.75 mm bore (72.626×30.162 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 3188/3120 reference at purchase.
- ABMA makes the 31.75×72.626 mm envelope interchangeable, not the ratings: NTN prints 93.5/98 kN for this execution and another make of the same number can differ in roller complement.
- Never drive the 72.626 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 (30.162 mm, the assembled cone-plus-cup width) with the cone width when drawing spacers; an abutment sized to T leaves the cup unseated.
- The 93.5/98 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-3188/3120; 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-3188/3120?
4T-3188/3120 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 31.75 mm bore (1.25 in), 72.626 mm outside diameter and 30.162 mm assembled width T (2.859 × 1.187 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 93.5 kN, C0 98 kN, grease limiting speed 5,500 r/min, oil speed 7,300 r/min, mass about 606 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-3188/3120 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 3188 cone or the 3120 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 93.5/98 kN ratings change with the cup.
What is the difference between 4T-3188/3120 and a metric ISO 355 tapered bearing?
4T-3188/3120 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 31.75×72.626×30.162 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-3188/3120 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 3188/3120 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-3188/3120 list two speeds, 5,500 and 7,300 r/min?
The lower figure, 5,500 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-3188/3120 at 7,300 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.