51108 bearing: complete specifications & equivalents
The 51108 is a ISO 104 radial bearing sized 40 x 60 x 13 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 | 60 mm |
| Width B | 13 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 26.9 kN |
| Basic static load rating C0 | 63 kN |
| Fatigue load limit Pu | 2.84 kN |
| Limiting speed (mechanical) | 3500 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 125 g |
| Manufacturer designation | NTN 51108 |
| 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 & 51100-series range
| Bore d | 1.575 in |
|---|---|
| Outer diameter D | 2.362 in |
| Width B | 0.512 in |
| ISO bore code | 08 |
| Radial section height (D−d)/2 | 10 mm |
| Smallest bore in 51100-series | 10 mm |
| Largest outer diameter in 51100-series | 640 mm |
| Width range across 51100-series | 9–85 mm |
| Bore position in 51100-series (smallest first) | 9 of 46 |
| Bore above smallest 51100-series size | 30 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51108-SKF | SKF | full Dimensions and internal design equivalent — standard interchange. | Identical ISO 15 envelope, seal and ratings band — standard interchange; re-verify precision class and clearance per supplier. |
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 51108 model number is decoded
At 40 x 60 x 13 mm, NTN 51108 sits in the light-section 51100 thrust family of the single-direction thrust programme. Decoding 51108: 511 is the dimension series (light-section 51100 thrust family), with 08 encodes the 40 mm bore (bore code x 5). The static margin, C0a 63 kN against Ca 26.9 kN, is what carries slow oscillating or shock thrust without permanent raceway dents. Choose the light-section 51100 thrust family when the shaft carries pure thrust in one direction at moderate speed — vertical shafts are the textbook case. After assembly, rotate under light load and check torque and temperature rise — a thrust ball bearing mounted with the washers swapped runs, but fails fast.
Typical equipment & failure modes
Common applications
- conveyor vertical-drive thrust positions
- vertical motor and pump thrust shoes
- machine-tool tailstock and steady-rest screws
- medium crane hook blocks and slewing jibs
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
- fretting between shaft washer and shaft when the seat is cut loose — the washer creeps, the centre line shifts and the balls start running off-track
- rapid flaking after radial load was allowed onto the bearing — a single-direction thrust ball bearing carries axial load only
- 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 511 light section is the speed-friendly end of the thrust-ball plan — for the same 40 mm bore it gives up load to gain OD, height and limiting-speed headroom.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51108 has no radial capacity at all.
- Never substitute a double-direction bearing drawing part-for-part: the single-direction 51108 stack height of 13 mm and washer set differ from the double-direction execution.
- Shock thrust above C0a 63 kN leaves dents that later become fatigue origins — crane-hook and press applications need the static check, not just the life calculation.
- The Ca 26.9/C0a 63 kN ratings and 2.84 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51108; 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 51108?
51108 is a single-direction thrust ball bearing to ISO 104: 40 mm shaft-washer bore, 60 mm outside diameter, 13 mm stack height (1.575 x 2.362 x 0.512 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 26.9 kN, C0a 63 kN and a 2.84 kN fatigue load limit Pu; the grease limiting speed is 3,500 r/min and the oil rating 5,000 r/min; mass about 125 g.
How is the 51108 designation structured?
511 is the dimension series (light-section 51100 thrust family); 08 encodes the 40 mm bore (bore code x 5). The 60 mm OD and 13 mm height follow the ISO 104 boundary plan for that series.
Can 51108 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 51108?
At the 3,500 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 51108?
The 40/60/13 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 26.9 kN / C0a 63 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.