231-850BK bearing: complete specifications & equivalents
The 231-850BK is a ISO 15 radial bearing sized 850 x 1360 x 400 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 850 mm |
| Outer diameter D | 1360 mm |
| Width B | 400 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 17300 kN |
| Basic static load rating C0 | 34000 kN |
| Fatigue load limit Pu | 1380 kN |
| Limiting speed (mechanical) | 170 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 2200000 g |
| Manufacturer designation | NTN 231/850BK |
| 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 | 33.465 in |
|---|---|
| Outer diameter D | 53.543 in |
| Width B | 15.748 in |
| ISO bore code | 31 |
| Radial section height (D−d)/2 | 255 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) | 35 of 36 |
| Bore above smallest 23100-series size | 750 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 231-850B | 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 231-850B — 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 231-850BK model number is decoded
The NTN order number 231/850BK identifies a 850×1360×400 mm (33.465 × 53.543 × 15.748 in) spherical roller bearing, 1:12 tapered bore (K), to the ISO 15 boundary plan. Numbering ties 231/850BK to its envelope and execution: same-number EA versus EM or plain variants share the 850 mm bore but differ in cage and sometimes mass, so they are quoted as separate articles. Two symmetric roller rows share the load: C 17300 kN, C0 34000 kN (C0/C ≈ 1.97), with useful axial capacity in either direction alongside the dominant radial load. Grease/oil ratio: the 170 r/min limiting value is .77 of the 220 r/min oil value; heavy 400 mm-wide cages run hot in churning grease, so quantity and groove supply both matter. 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 850 mm set.
Typical equipment & failure modes
Common applications
- large wind-turbine main-shaft arrangements
- steel-mill and heavy crusher main shafts
- mining shovel and dragline swing shafts
- cement-rotary-kiln support and trunnion rolls
Known failure patterns
- lubricant starvation at the centre rib area when the D1/W33 groove is not connected to a relubrication supply
- machined EM cage wear from inadequate oil film at the cage-guiding surfaces
- sliding wear and heat when relubrication intervals ignore the groove (D1/W33) supply path
- false brinelling on stopped machines exposed to screen or crusher vibration
- asymmetric wear on the two roller rows from sustained angular misalignment beyond the self-aligning range
Selection pitfalls — read before you substitute
- At 850 mm bore 231/850BK 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.
- Never substitute 231/850BK by envelope alone: the 34000 kN C0 and 1380 kN Pu are specific to the NTN basic execution, and vibrating duty depends heavily on cage identity.
- The two roller rows must share load equally — a tilted spacer or unequal abutment on the 400 mm-wide ring loads one row only and shows as asymmetric race polish during inspection.
- 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 850 mm bearing, and drive-up procedures differ.
- Adapter-sleeve mounting requires the correct sleeve series and locknut for the 850 mm shaft; a sleeve sized to bore alone ignores thread, width and the oil-injection option on large K30 seats.
- The 17300/34000 kN ratings, 1380 kN Pu and 2200000 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 231/850BK (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 231/850BK?
231/850BK is an NTN double-row spherical roller bearing to ISO 15: 850 mm bore, 1360 mm OD and 400 mm width (33.465 × 53.543 × 15.748 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 17300 kN, C0 34000 kN, Pu 1380 kN, grease limiting speed 170 r/min, oil 220 r/min, mass about 2200000 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. 231/850BK 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 231/850B.
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. 231/850BK is the basic execution.
What do D1 and W33 mean on 231/850BK?
231/850BK 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 231/850BK 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 — 17300 kN C / 34000 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.