2688-2631 bearing: complete specifications & equivalents
The 2688-2631 is a ANSI ABMA 19.2 radial bearing sized 26.988 x 66.421 x 23.812 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 26.988 mm |
| Outer diameter D | 66.421 mm |
| Width B | 23.812 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 71.5 kN |
| Basic static load rating C0 | 72.5 kN |
| Limiting speed (mechanical) | 6200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 429 g |
| Manufacturer designation | NTN 4T-2688/2631 |
| 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 | 1.063 in |
|---|---|
| Outer diameter D | 2.615 in |
| Width B | 0.937 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 19.7 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) | 22 of 148 |
| Bore above smallest 4t-inch-series size | 14.288 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 2688 | 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 2688-2631 model number is decoded
4T-2688/2631 belongs to the NTN inch 4T tapered roller range (pure-numeric inch family); cone and cup are ordered by their own references and are individually interchangeable with like-numbered parts. 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 — 2688 sits in the pure-numeric inch family. Selection: C 71.5 kN against C0 72.5 kN gives a C0/C ratio of 1.01 for the 26.988 mm bore; the pair is counted as one adjusted unit when checking L10 at the equivalent combined load. Housing fitment sequence for 4T-2688/2631: press the 2631 cup square into the 66.421 mm seat first, then bring the 2688 cone (on its 26.988 mm shaft) into adjustment — the two references are separate engineering parts that happen to ship as one set. After bedding-in, re-check the end play of the adjusted 4T-2688/2631 pair — initial seating of the ring faces relaxes the setting slightly.
Typical equipment & failure modes
Common applications
- machine-tool headstocks on inch spindles
- pump and blower drive shafts with combined load
- truck and trailer axle hubs on inch-dimensioned axles
- agricultural tractor transmission and PTO shafts
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
- cage fatigue when the pair runs continuously near the grease limiting speed without oil cooling
- 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 26.988 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-2688/2631.
- The pure-numeric inch family at 26.988 mm bore (66.421×23.812 mm assembled) is one of several inch families sharing similar bores; cross-series swaps change OD, T and contact angle, so match the full 2688/2631 reference at purchase.
- Shaft and housing fillets must clear the ring chamfers of 2688 and 2631; use undercut shoulders so the rings seat on the face, not on a radius.
- Shaft and housing fillets must clear the ring chamfers of 2688 and 2631; use undercut shoulders so the rings seat on the face, not on a radius.
- Grease packs must leave free volume inside the 23.812 mm-wide set; over-greasing a pair churning near the oil-band speed of 8,200 r/min raises temperature and destroys the setting.
- The 71.5/72.5 kN ratings here are NTN Ball and Roller Bearings CAT.No.2203E figures for 4T-2688/2631; 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-2688/2631?
4T-2688/2631 is an inch-series single-row tapered roller bearing to the ABMA boundary plan: 26.988 mm bore (1.063 in), 66.421 mm outside diameter and 23.812 mm assembled width T (2.615 × 0.937 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 71.5 kN, C0 72.5 kN, grease limiting speed 6,200 r/min, oil speed 8,200 r/min, mass about 429 g. It is an open, separable cone/cup set with a pressed-steel cage.
Are the cone and cup of 4T-2688/2631 interchangeable separately?
Yes — ABMA inch parts are individually interchangeable: the 2688 cone or the 2631 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 71.5/72.5 kN ratings change with the cup.
What is the difference between 4T-2688/2631 and a metric ISO 355 tapered bearing?
4T-2688/2631 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 26.988×66.421×23.812 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-2688/2631 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 2688/2631 references; the 4T spelling is retained among this page's search aliases.
Why does 4T-2688/2631 list two speeds, 6,200 and 8,200 r/min?
The lower figure, 6,200 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-2688/2631 at 8,200 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.