21308C bearing: complete specifications & equivalents
The 21308C 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 | 705 g |
| Manufacturer designation | NTN 21308C |
| 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 |
|---|---|---|---|
| 21308CK | NTN | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same NTN 21300-series envelope, cage and ratings; this is the cylindrical-bore execution of the tapered-bore 21308CK (K/K30 sleeve or tapered-seat mounting). 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 21308C model number is decoded
21308C is an NTN double-row spherical roller bearing: two rows of symmetric rollers on a sphered outer raceway, 40×90×23 mm to ISO 15, with pressed-steel cage of the 213-series C design. On the NTN nameplate the suffix cluster after the size reads in order: cage design (C/CK), bore (cylindrical), lubrication feature (none); 21308C is assembled exactly in that order. The bearing accepts predominantly radial load with a moderate axial share, but is not a pure thrust bearing: sustained axial-only load skids the unloaded row and damages the C design-code cage. Pu 12.6 kN against C0 90 kN anchors the contamination derating; for dirty mining duty the adjusted life of 21308C moves with cleanliness far more than with small C variations. 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
- marine propulsion auxiliary shafts
- vibrating screen and feeder shafts
- industrial gearbox and reducer shafts
- conveyor pulley and elevator drum shafts
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
- micro-pitting when the EHL film is thinner than the raceway composite roughness
- brinelling from static overload or a hammer blow during sleeve mounting
- 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 21308C is greased for life.
- 213-series C/CK executions use the C cage/design code — CK adds the 1:12 tapered bore; quote 21308C in full because a C cannot be mounted on an adapter-sleeve tapered seat.
- 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 40 mm bearing, and drive-up procedures differ.
- Self-aligning does not mean unlimited misalignment: beyond the catalogue angle the outer ring's spherical travel is exhausted and the 98 kN rating no longer applies.
- Never substitute 21308C 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 98/90 kN ratings, 12.6 kN Pu and 705 g mass are NTN Ball and Roller Bearings CAT.No.2203E values for 21308C (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 21308C?
21308C 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 705 g. It is open, with pressed-steel cage of the 213-series C design.
What is the difference between the K/K30 tapered bore and the cylindrical bore versions?
21308C has a cylindrical bore and mounts directly on a machined shaft seat. Its tapered-bore counterpart is 21308CK (K = 1:12, or K30 = 1:30 on the wide series), intended for adapter/withdrawal-sleeve mounting.
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. 21308C is the C design-code execution.
What do D1 and W33 mean on 21308C?
21308C 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 21308C 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.