231-750BK bearing: complete specifications & equivalents
The 231-750BK is a ISO 15 radial bearing sized 750 x 1220 x 365 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 750 mm |
| Outer diameter D | 1220 mm |
| Width B | 365 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 14300 kN |
| Basic static load rating C0 | 27200 kN |
| Fatigue load limit Pu | 1130 kN |
| Limiting speed (mechanical) | 200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1650000 g |
| Manufacturer designation | NTN 231/750BK |
| Standard | ISO 15 |
| Catalog version | NTN Ball and Roller Bearings CAT.No.2203E |
| Last verified | 2026-10-01 |
Source: catalog reference (NTN Ball and Roller Bearings CAT.No.2203E) · extracted 2026-10-01
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (NTN Ball and Roller Bearings CAT.No.2203E); 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 & 23100-series range
| Bore d | 29.528 in |
|---|---|
| Outer diameter D | 48.031 in |
| Width B | 14.37 in |
| ISO bore code | 31 |
| Radial section height (D−d)/2 | 235 mm |
| Smallest bore in 23100-series | 100 mm |
| Largest outer diameter in 23100-series | 1420 mm |
| Width range across 23100-series | 52–412 mm |
| Bore position in 23100-series (smallest first) | 33 of 36 |
| Bore above smallest 23100-series size | 650 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 231-750B | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same NTN 23100-series envelope, cage and ratings; this is the tapered-bore execution (K, 1:12) of the cylindrical-bore 231-750B — mounting (adapter/withdrawal sleeve or tapered seat, drive-up) differs. Verify shaft arrangement. |
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 231-750BK model number is decoded
For heavy radial load with misalignment on a 750 mm shaft, NTN supplies 231/750BK: sphered outer raceway, two roller rows, pressed-steel cage (standard execution), oil speed 260 r/min. Reading the full code: the number gives the 750×1220 mm envelope, — names the cage/capacity execution, K marks the 1:12 tapered bore for adapter/withdrawal-sleeve mounting, and plain outer ring (no D1/W33 groove) completes the order number. The plain outer ring (no D1/W33 groove) makes relubrication part of the design: fresh grease reaches the rolling elements through the outer-ring feature rather than relying solely on end-side packing. 750 mm bore is 29.528 in and 1220 mm OD is 48.031 in; the ISO 15 envelope swaps between brands, but the 14300/27200 kN ratings and cage design are NTN 2203E values. After mounting on a tapered seat, lock the nut and re-check clearance after a short running-in period, because sleeve seating and ring lift-off can change the residual clearance of the 750 mm set.
Typical equipment & failure modes
Common applications
- large SAG/ball-mill trunnion and pinion shafts
- heavy vibrating screens and grizzly feeders
- offshore and marine propulsion shaftlines
- large wind-turbine main-shaft arrangements
Known failure patterns
- lubricant starvation at the centre rib area when the D1/W33 groove is not connected to a relubrication supply
- pressed EA cage fatigue under sustained vibration when minimum load is not maintained
- sliding wear and heat when relubrication intervals ignore the groove (D1/W33) supply path
- brinelling from static overload or a hammer blow during sleeve mounting
- water-induced pitting in washdown or outdoor duty without effective external seals
Selection pitfalls — read before you substitute
- At 750 mm bore 231/750BK is normally mounted on adapter/withdrawal sleeves with hydraulic assistance; follow the NTN drive-up angle or oil-injection procedure — manual nut tightening cannot set the multi-tonne seating correctly.
- Open spherical rollers swallow dust in mining duty; specify labyrinth or taconite seals externally, or the 200 r/min grease rating is lost to abrasive wear long before fatigue.
- Self-aligning does not mean unlimited misalignment: beyond the catalogue angle the outer ring's spherical travel is exhausted and the 14300 kN rating no longer applies.
- Never substitute 231/750BK by envelope alone: the 27200 kN C0 and 1130 kN Pu are specific to the NTN basic execution, and vibrating duty depends heavily on cage identity.
- K and K30 are different tapers — K is 1:12 and K30 is 1:30 on the wide series; an adapter sleeve for one will not mount the other 750 mm bearing, and drive-up procedures differ.
- The 14300/27200 kN ratings, 1130 kN Pu and 1650000 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 231/750BK (basic); another maker's same-envelope part revises internal geometry, so re-verify ratings and cage before substitution on vibrating or rated drives.
Frequently asked questions
What are the dimensions and catalogue data of 231/750BK?
231/750BK is an NTN double-row spherical roller bearing to ISO 15: 750 mm bore, 1220 mm OD and 365 mm width (29.528 × 48.031 × 14.37 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 14300 kN, C0 27200 kN, Pu 1130 kN, grease limiting speed 200 r/min, oil 260 r/min, mass about 1650000 g. It is open, with pressed-steel cage (standard execution) and a 1:12 tapered bore.
What is the difference between the K/K30 tapered bore and the cylindrical bore versions?
K denotes a 1:12 tapered bore. 231/750BK mounts on an adapter sleeve (or tapered shaft seat) and is driven up to the specified residual clearance; its cylindrical-bore counterpart in the same envelope and ratings is 231/750B.
What do EA and EM mean on NTN spherical roller bearings?
EA is the NTN standard-capacity/high-capacity execution with a pressed sheet-steel window cage; EM is the high-capacity execution with a one-piece machined brass cage. Both use the optimised symmetric-roller design, but cage identity changes mass, speed behaviour and suitability for duties like vibrating screens, so they are separate order numbers. 231/750BK is the basic execution.
What do D1 and W33 mean on 231/750BK?
231/750BK is listed without a D1/W33 outer-ring groove in 2203E; lubrication is supplied from the ring sides. D1 (NTN spelling) and W33 add the annular groove plus holes and are ordered as distinct suffixed executions of the same envelope.
How much misalignment and axial load can 231/750BK take?
The sphered outer raceway compensates static and dynamic misalignment in the order of 1–2° (verify the exact 2203E figure for the 23100 series); beyond that, load concentrates on one roller row. Load is predominantly radial with a moderate axial share in either direction — 14300 kN C / 27200 kN C0 — but sustained pure axial load is not recommended because it unloads one row.
Reviewed & verified by the MPN Base engineering desk against source catalog NTN Ball and Roller Bearings CAT.No.2203E on 2026-10-01. Read our editorial & correction policy.