1203 bearing: complete specifications & equivalents
The 1203 is a ISO 15 radial bearing sized 17 x 40 x 12 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 17 mm |
| Outer diameter D | 40 mm |
| Width B | 12 mm |
| Seal / shield | open |
| Basic dynamic load rating C | 8 kN |
| Basic static load rating C0 | 2.01 kN |
| Fatigue load limit Pu | 0.083 kN |
| Limiting speed (mechanical) | 16000 rpm |
| Mass | 74 g |
| Manufacturer designation | 1203S |
| 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 | 0.669 in |
|---|---|
| Outer diameter D | 1.575 in |
| Width B | 0.472 in |
| ISO bore code | 03 |
| Radial section height (D−d)/2 | 11.5 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) | 4 of 23 |
| Bore above smallest 1200-series size | 7 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 1203 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: 1203 carries bore code 03 = 17 mm. Codes 00–03 follow the 10/12/15/17 mm exception table rather than code × 5. Outside diameter 40 mm and width 12 mm follow the ISO 15 general plan. The cylindrical bore fits directly on a machined shaft seat; a tapered-bore K variant is available for adapter-sleeve mounting. 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
- small pump impeller shafts
- garden equipment and light machinery
- instrument and office machine drives
- small electric motor and fan shafts
Known failure patterns
- contamination wear from dust and dirt ingress through the open arrangement
- lubricant starvation when no regreasing interval is maintained
- edge loading and stress concentration from excessive misalignment beyond the allowable angle
- raceway smearing under marginal lubrication at start-up
Selection pitfalls — read before you substitute
- Bore codes 00–03 use the exception table: 1203 fits a 17 mm shaft — the code × 5 mnemonic does not apply below code 04 (it would imply 0 mm for code 00).
- The 12xx light section at 17 mm bore uses a smaller 40 mm OD than a 1303; load ratings are lower, so do not replace a failed 13-series bearing with a 12-series without re-rating the load.
- The open 1203 has no lubricant retention: grease escapes and contaminants migrate straight into the 17×40×12 mm raceway, so specify a sealed arrangement for dusty or washdown duty.
- Open bearings tolerate the highest speeds in the 1200-series but need a defined regreasing interval; run-to-failure lubrication is the dominant cause of early failure in open 1203 units.
- Do not use a self-aligning ball bearing where high radial rigidity is required — the sphered outer raceway allows more radial movement than a deep-groove or cylindrical roller bearing.
Frequently asked questions
What are the dimensions of a 1203 self-aligning ball bearing?
A 1203 self-aligning ball bearing has a 17 mm bore, 40 mm outer diameter and 12 mm width, per ISO 15 boundary dimensions. This is the cylindrical-bore version; a tapered-bore K variant is available for adapter-sleeve mounting.
Why does 1203 not follow the bore-code × 5 rule?
Codes 00–03 use the exception table (10, 12, 15 and 17 mm): 1203 with code 03 has a 17 mm bore. The code × 5 convention starts at code 04 (20 mm).
What does the open suffix mean on 1203?
A bare 1203 designation means open: no shields or seals, normal CN radial clearance and P0 normal tolerance unless further suffixes are ordered. The application must supply and retain the lubrication.
How does the 1200 compare with other self-aligning series at the same 17 mm bore?
The 12xx is the light section: 40×12 mm with an 11.5 mm radial section at 17 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.