51115 bearing: complete specifications & equivalents
The 51115 is a ISO 104 radial bearing sized 75 x 100 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 | 75 mm |
| Outer diameter D | 100 mm |
| Width B | 19 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 44.5 kN |
| Basic static load rating C0 | 136 kN |
| Fatigue load limit Pu | 6.15 kN |
| Limiting speed (mechanical) | 2200 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 399 g |
| Manufacturer designation | NTN 51115 |
| 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 | 2.953 in |
|---|---|
| Outer diameter D | 3.937 in |
| Width B | 0.748 in |
| ISO bore code | 15 |
| Radial section height (D−d)/2 | 12.5 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) | 16 of 46 |
| Bore above smallest 51100-series size | 65 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51115-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 51115 model number is decoded
At 75 x 100 x 19 mm, NTN 51115 sits in the light-section 51100 thrust family of the single-direction thrust programme. Two fields make up the code — 511 is the dimension series (light-section 51100 thrust family) and 15 encodes the 75 mm bore (bore code x 5). At 19 mm of height the stack is compact for the 75 mm bore class, trading section height for the light-section load level. The 75/100/19 envelope follows ISO 104, so dimensional interchange holds between makers — raceway osculation and ratings do not automatically follow. The shaft washer (bore 75 mm, tight on the shaft) and the housing washer (slightly looser bore) are not interchangeable — check the catalogue bore codes before pressing anything on.
Typical equipment & failure modes
Common applications
- large crane hook and swivel assemblies
- rolling-mill screwdown and adjustment screws
- heavy press and forging-machine thrust seats
- ship winch and capstan thrust shafts
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
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
- cage breakage after repeated shock reversal banged the ball set against the pocket bridges
Selection pitfalls — read before you substitute
- At 75 mm bore the washers are heavy enough to sag out of square during assembly — support the stack horizontally where possible and verify face runout before loading.
- The 511 light section is the speed-friendly end of the thrust-ball plan — for the same 75 mm bore it gives up load to gain OD, height and limiting-speed headroom.
- Swapping the shaft and housing washers is an easy assembly error on the 75 mm size — the bores differ only slightly, but the wrong pairing walks off-centre under load.
- Do not reuse a thrust bearing to "absorb" shaft thermal growth — the bearing clamps axially, so growth must be handled on the radial-bearing side of the arrangement.
- Below the minimum axial load the balls skid; the catalogue Ca of 44.5 kN never saves a bearing that is running too lightly loaded at 2,200 r/min.
- The Ca 44.5/C0a 136 kN ratings and 6.15 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51115; 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 51115?
51115 is a single-direction thrust ball bearing to ISO 104: 75 mm shaft-washer bore, 100 mm outside diameter, 19 mm stack height (2.953 x 3.937 x 0.748 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 44.5 kN, C0a 136 kN and a 6.15 kN fatigue load limit Pu; the grease limiting speed is 2,200 r/min and the oil rating 3,200 r/min; mass about 399 g.
How is the 51115 designation structured?
511 is the dimension series (light-section 51100 thrust family); 15 encodes the 75 mm bore (bore code x 5). The 100 mm OD and 19 mm height follow the ISO 104 boundary plan for that series.
Can 51115 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 51115?
At the 2,200 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 51115?
The 75/100/19 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 44.5 kN / C0a 136 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.