21308CK bearing: complete specifications & equivalents
The 21308CK is a ISO 15 radial bearing sized 40 x 90 x 23 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 40 mm |
| Outer diameter D | 90 mm |
| Width B | 23 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Cage | steel |
| Basic dynamic load rating C | 98 kN |
| Basic static load rating C0 | 90 kN |
| Fatigue load limit Pu | 12.6 kN |
| Limiting speed (mechanical) | 4900 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 694 g |
| Manufacturer designation | NTN 21308CK |
| 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 & 21300-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 0.906 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 25 mm |
| Smallest bore in 21300-series | 40 mm |
| Largest outer diameter in 21300-series | 240 mm |
| Width range across 21300-series | 23–50 mm |
| Bore position in 21300-series (smallest first) | 1 of 14 |
| Bore above smallest 21300-series size | 0 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 21308C | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same NTN 21300-series envelope, cage and ratings; this is the tapered-bore execution (K, 1:12) of the cylindrical-bore 21308C — 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 21308CK model number is decoded
21308CK is the C design-code execution of NTN's spherical roller range for a 40 mm shaft — 98 kN basic dynamic capacity in a 694 g, open ISO 15 envelope. The leading digits are the ISO 15 dimension series (21300 series); the bore code resolves to 40 mm (two-digit code ×5, with the 00–03 exception table), and 90 mm OD / 23 mm width follow the general plan. The sphered outer raceway lets the inner-ring assembly pivot, accommodating shaft deflection and housing misalignment (around 1–2° for this class; use the 2203E value for the exact series) without edge loading the rollers. Catalogue mass 694 g (0.69 kg) for the 40×90×23 mm execution includes the C design-code cage and both roller rows; shaft and housing shoulders must support that ring squarely. Check the self-aligning movement after fitting: the housing should pivot freely around the sphered outer raceway; a pinched outer ring removes the alignment capacity the bearing was selected for.
Typical equipment & failure modes
Common applications
- stone crusher and screen eccentric shafts
- papermaking and printing press rolls
- pump and fan shafts under heavy belt load
- marine propulsion auxiliary shafts
Known failure patterns
- raceway spalling at the roller ends when misalignment or deflection concentrates the line contact
- machined EM cage wear from inadequate oil film at the cage-guiding surfaces
- roller-end smearing during skidding starts under light load and high viscosity grease
- water-induced pitting in washdown or outdoor duty without effective external seals
- fretting corrosion between adapter sleeve and tapered bore when the drive-up is insufficient
Selection pitfalls — read before you substitute
- Vibrating-duty 40 mm bearings need the right clearance class and secure fits; verify the k5/m5 seat and relubrication routing rather than assuming the open 21308CK is greased for life.
- Never substitute 21308CK by envelope alone: the 90 kN C0 and 12.6 kN Pu are specific to the NTN C design-code 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 23 mm-wide ring loads one row only and shows as asymmetric race polish during inspection.
- 213-series C/CK executions use the C cage/design code — CK adds the 1:12 tapered bore; quote 21308CK in full because a C cannot be mounted on an adapter-sleeve tapered seat.
- Minimum load must be maintained even at rest under vibration: an unloaded 21308CK on a stopped screen false-brinells; parking brakes and shaker isolation both matter.
- The 98/90 kN ratings, 12.6 kN Pu and 694 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 21308CK (C design-code); 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 21308CK?
21308CK is an NTN double-row spherical roller bearing to ISO 15: 40 mm bore, 90 mm OD and 23 mm width (1.575 × 3.543 × 0.906 in). From NTN Ball and Roller Bearings CAT.No.2203E: C 98 kN, C0 90 kN, Pu 12.6 kN, grease limiting speed 4,900 r/min, oil 6,400 r/min, mass about 694 g. It is open, with pressed-steel cage of the 213-series C design 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. 21308CK 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 21308C.
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. 21308CK is the C design-code execution.
What do D1 and W33 mean on 21308CK?
21308CK 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 21308CK take?
The sphered outer raceway compensates static and dynamic misalignment in the order of 1–2° (verify the exact 2203E figure for the 21300 series); beyond that, load concentrates on one roller row. Load is predominantly radial with a moderate axial share in either direction — 98 kN C / 90 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.