51208 bearing: complete specifications & equivalents
The 51208 is a ISO 104 radial bearing sized 40 x 68 x 19 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 | 68 mm |
| Width B | 19 mm |
| Seal / shield | open |
| Basic dynamic load rating C | 47 kN |
| Basic static load rating C0 | 98.5 kN |
| Fatigue load limit Pu | 4.45 kN |
| Limiting speed (mechanical) | 2700 rpm |
| Mass | 276 g |
| Manufacturer designation | 51208 |
| Standard | ISO 104 |
| 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 & 51200-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 2.677 in |
| Width B | 0.748 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 14 mm |
| Smallest bore in 51200-series | 10 mm |
| Largest outer diameter in 51200-series | 150 mm |
| Width range across 51200-series | 11–38 mm |
| Bore position in 51200-series (smallest first) | 9 of 20 |
| Bore above smallest 51200-series size | 30 mm |
Cross references & equivalents
No verified interchange data yet. Send an inquiry and our team will confirm equivalents manually.
How the 51208 model number is decoded
In the 51200-series (ISO 104 dimension series) the leading digits 512 mark a single-direction thrust ball bearing and the last two digits encode the bore: 51208 carries bore code 08 = 40 mm. The ISO 104 boundary dimensions are 40 mm bore, 68 mm outside diameter and 19 mm height. Two flat washers (shaft and housing) and a ball cage assembly allow the bearing to carry pure axial load in one direction while accommodating minor misalignment.
Typical equipment & failure modes
Common applications
- electric motor axial positioning
- pump and compressor thrust support
- gearbox axial load management
- conveyor drive thrust washers
Known failure patterns
- washer seat fretting from a loose housing or shaft fit
- rolling-contact fatigue spalling after the rated L10 life is exceeded
- cage wear or fracture from sustained vibration or shock loading
Selection pitfalls — read before you substitute
- At a 40 mm bore, check shaft shoulder runout before fitting 51208; a skewed shoulder tilts the shaft washer and concentrates load on a few balls.
- The 512xx medium-light section at 40 mm bore is the default general-purpose thrust bearing; before upgrading to a 513xx for extra capacity, confirm the housing accepts a 68 mm OD and 19 mm height.
- Thrust ball bearings carry axial load only — never apply radial load to 51208; the flat washers will skid and score.
- Do not use a thrust ball bearing for combined radial-axial loads — pair it with a radial bearing (deep-groove or spherical roller) for the radial component.
Frequently asked questions
What are the dimensions of a 51208 thrust ball bearing?
A 51208 thrust ball bearing has a 40 mm bore, 68 mm outside diameter and 19 mm height, per ISO 104 boundary dimensions. It consists of a shaft washer, housing washer and ball cage assembly.
How does the 51208 bore code work?
The last two digits of 51208 are bore code 08, giving 08 × 5 = 40 mm bore. The 68 mm outside diameter and 19 mm height follow the ISO 104 dimension series, not the bore code alone.
Can a 51208 thrust ball bearing carry radial load?
No. Single-direction thrust ball bearings carry axial load only. Any radial component must be supported by a separate radial bearing (deep-groove, cylindrical roller or spherical roller).
How does the 51200 compare with other thrust series at the same 40 mm bore?
The 512xx is the medium-light section: 68×19 mm, 14.0 mm radial section at 40 mm bore. A 513xx on the same bore is larger and higher-rated; a 511xx is smaller and lower-rated.
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.