1211K bearing: complete specifications & equivalents
The 1211K is a ISO 15 radial bearing sized 55 x 100 x 21 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 55 mm |
| Outer diameter D | 100 mm |
| Width B | 21 mm |
| Seal / shield | open |
| Basic dynamic load rating C | 26.9 kN |
| Basic static load rating C0 | 10 kN |
| Fatigue load limit Pu | 0.4 kN |
| Limiting speed (mechanical) | 6000 rpm |
| Mass | 708 g |
| Manufacturer designation | 1211SK |
| Standard | ISO 15 |
| Catalog version | CAT. No. 2203-3/E 2024 |
| Last verified | 2026-09-25 |
Source: catalog reference (CAT. No. 2203-3/E 2024) · extracted 2026-09-25
Parameters extracted from the official NTN Ball and Roller Bearings catalogue (CAT. No. 2203-3/E 2024); 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 & 1200-series range
| Bore d | 2.165 in |
|---|---|
| Outer diameter D | 3.937 in |
| Width B | 0.827 in |
| ISO bore code | — |
| Radial section height (D−d)/2 | 22.5 mm |
| Smallest bore in 1200-series | 10 mm |
| Largest outer diameter in 1200-series | 200 mm |
| Width range across 1200-series | 9–38 mm |
| Bore position in 1200-series (smallest first) | 12 of 23 |
| Bore above smallest 1200-series size | 45 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 1211K model number is decoded
In the 1200-series (ISO 15 dimension series) the leading digits 12 mark a double-row self-aligning ball bearing and the last two digits encode the bore: 1211 carries bore code 11 = 55 mm. Outside diameter 100 mm and width 21 mm follow the ISO 15 general plan. The K suffix denotes a 1:12 tapered bore for mounting on an adapter sleeve or tapered shaft seat; the cylindrical-bore equivalent is 1211. Two rows of balls run on a common sphered outer raceway, allowing the inner ring to pivot and compensate for shaft deflection or housing misalignment.
Typical equipment & failure modes
Common applications
- industrial electric motor shafts
- pump and compressor drive shafts
- gearbox and speed reducer shafts
- conveyor and material handling drives
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- false brinelling from vibration while the shaft is stationary
- edge loading and stress concentration from excessive misalignment beyond the allowable angle
Selection pitfalls — read before you substitute
- Temperature rise and interference fits consume internal clearance on this 55 mm bore: a CN bearing on a tight, hot shaft can lose all residual clearance — size 1211 with C3 for those conditions.
- The 12xx light section at 55 mm bore uses a smaller 100 mm OD than a 1311; load ratings are lower, so do not replace a failed 13-series bearing with a 12-series without re-rating the load.
- Tapered-bore 1211K requires a matching adapter sleeve (e.g. H2xx for small bores, H3xx for larger); verify the sleeve bore code matches the 55 mm shaft before ordering.
- The adapter sleeve adds length and a small radial step; check that the housing bore and shaft shoulder clear the sleeve nut and that the withdrawal nut is accessible for future dismounting.
- The self-aligning feature compensates for static misalignment and shaft deflection, not for poor initial alignment — always align shaft and housing as accurately as possible before fitting 1211K.
Frequently asked questions
What are the dimensions of a 1211K self-aligning ball bearing?
A 1211K self-aligning ball bearing has a 55 mm bore, 100 mm outer diameter and 21 mm width, per ISO 15 boundary dimensions. The K suffix indicates a 1:12 tapered bore for adapter-sleeve mounting; the cylindrical-bore version is 1211.
How does the 1211 bore code work?
The last two digits of 1211 are bore code 11, giving 11 × 5 = 55 mm bore. The 100 mm outside diameter and 21 mm width follow the ISO 15 diameter series, not the bore code alone.
What does the K suffix mean on 1211K?
The K suffix denotes a 1:12 tapered bore for mounting with an adapter sleeve. The cylindrical-bore equivalent is 1211. Adapter sleeves are sold separately and must match the bore code.
How does the 1200 compare with other self-aligning series at the same 55 mm bore?
The 12xx is the light section: 100×21 mm with a 22.5 mm radial section at 55 mm bore — below 13/22/23 in load capacity, for light loads in compact spaces.
Reviewed & verified by the MPN Base engineering desk against source catalog CAT. No. 2203-3/E 2024 on 2026-09-25. Read our editorial & correction policy.