51408 bearing: complete specifications & equivalents
The 51408 is a ISO 104 radial bearing sized 40 x 90 x 36 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 | 36 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 112 kN |
| Basic static load rating C0 | 205 kN |
| Fatigue load limit Pu | 9.25 kN |
| Limiting speed (mechanical) | 1700 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1080 g |
| Manufacturer designation | NTN 51408 |
| Standard | ISO 104 |
| 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 & 51400-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 3.543 in |
| Width B | 1.417 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 25 mm |
| Smallest bore in 51400-series | 25 mm |
| Largest outer diameter in 51400-series | 300 mm |
| Width range across 51400-series | 24–120 mm |
| Bore position in 51400-series (smallest first) | 4 of 20 |
| Bore above smallest 51400-series size | 15 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51408-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 40×90×36 mm envelope per ISO 15; catalogue load ratings differ by >10% — re-rate the application before substituting. |
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 51408 model number is decoded
The extra-heavy 51400 thrust family entry 51408 stacks a shaft washer, ball-and-cage set and housing washer into 36 mm of height over a 40 mm bore. Decoding 51408: 514 is the dimension series (extra-heavy 51400 thrust family), with 08 encodes the 40 mm bore (bore code x 5). On speed, the grease limiting speed is 1,700 r/min and the oil rating 2,500 r/min. If the duty is high speed with light thrust, check the minimum axial load formula first; a too-large thrust ball bearing fails by skid long before its Ca of 112 kN is ever approached. Mount the stack in order and confirm the shaft washer sits against its shoulder before loading: pressing through the balls brinells the raceway on the spot.
Typical equipment & failure modes
Common applications
- vertical motor and pump thrust shoes
- machine-tool tailstock and steady-rest screws
- medium crane hook blocks and slewing jibs
- extruder and mixer thrust housings
Known failure patterns
- ball and raceway smearing from gyroscopic spin when the bearing runs fast under too little axial load — the minimum-load rule exists exactly for this
- housing-washer rocking on an out-of-square support face, seen as uneven wear around the raceway circle and rising running torque
- early fatigue from thrust reversal hammering the unloaded raceway, because the bearing has no contact surfaces for the opposite direction
- contamination pitting from particles settling on the horizontal housing washer — the classic failure of vertical-shaft grease-lubricated seats
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
Selection pitfalls — read before you substitute
- In this size class the frequent miss is washer identification: keep the catalogued shaft/housing washer pairing of the 40 mm size together from unpacking to assembly.
- The 514 extra-heavy section is the top of the thrust-ball plan at this bore; beyond it the catalogue moves to spherical roller thrust bearings.
- Grease in a horizontal-washer seat stays only if the housing is designed to hold it; open vertical arrangements need an oil bath or a grease-retaining cover.
- Grease in a horizontal-washer seat stays only if the housing is designed to hold it; open vertical arrangements need an oil bath or a grease-retaining cover.
- A housing washer pressed tight in its seat cannot self-centre; the resulting eccentric running shows up as cage wear long before raceway fatigue.
- The Ca 112/C0a 205 kN ratings and 9.25 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51408; raceway geometry legitimately differs between manufacturers, so re-verify ratings and washer identification before substituting another make.
Frequently asked questions
What are the dimensions and catalogue ratings of NTN 51408?
51408 is a single-direction thrust ball bearing to ISO 104: 40 mm shaft-washer bore, 90 mm outside diameter, 36 mm stack height (1.575 x 3.543 x 1.417 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 112 kN, C0a 205 kN and a 9.25 kN fatigue load limit Pu; the grease limiting speed is 1,700 r/min and the oil rating 2,500 r/min; mass about 1080 g.
How is the 51408 designation structured?
514 is the dimension series (extra-heavy 51400 thrust family); 08 encodes the 40 mm bore (bore code x 5). The 90 mm OD and 36 mm height follow the ISO 104 boundary plan for that series.
Can 51408 carry radial load or reversing thrust?
No. The raceways contact the balls at 90 deg to the shaft, so the rating is purely axial and single-direction. Radial load must be carried by a separate radial bearing, and reversing thrust needs a second thrust bearing or a double-direction execution.
Why does NTN specify a minimum axial load for 51408?
At the 1,700 r/min class speed, centrifugal and gyroscopic effects make an under-loaded ball set skid and smear instead of roll. The catalogue minimum-load formula gives the axial preload — from the machine weight, springs or a dead-weight — that keeps the contact rolling.
What should be checked before substituting another make for 51408?
The 40/90/36 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 112 kN / C0a 205 kN, the speed figures and the shaft/housing washer identification against the donor catalogue.
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.