51111 bearing: complete specifications & equivalents
The 51111 is a ISO 104 radial bearing sized 55 x 78 x 16 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 55 mm |
| Outer diameter D | 78 mm |
| Width B | 16 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 35 kN |
| Basic static load rating C0 | 93 kN |
| Fatigue load limit Pu | 4.2 kN |
| Limiting speed (mechanical) | 2800 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 226 g |
| Manufacturer designation | NTN 51111 |
| 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 | 2.165 in |
|---|---|
| Outer diameter D | 3.071 in |
| Width B | 0.63 in |
| ISO bore code | 11 |
| Radial section height (D−d)/2 | 11.5 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) | 12 of 46 |
| Bore above smallest 51100-series size | 45 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51111-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 55×78×16 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 51111 model number is decoded
51111 is an NTN single-direction thrust ball bearing of the light-section 51100 thrust family: 55 mm bore, 78 mm outside diameter, 16 mm overall height in NTN Ball and Roller Bearings CAT.No.2203E. Decoding 51111: 511 is the dimension series (light-section 51100 thrust family), with 11 encodes the 55 mm bore (bore code x 5). On speed, the grease limiting speed is 2,800 r/min and the oil rating 4,000 r/min. Size selection ends with the minimum-load check: at the 2,800 r/min class speed, the balls need a defined axial preload to keep rolling instead of skidding. Keep the support faces square: a housing face out of perpendicular by a few hundredths over the 78 mm OD already tilts the raceway and concentrates the 93 kN static capacity on a few balls.
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
- 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
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
- 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 55 mm size together from unpacking to assembly.
- The 511 light section is the speed-friendly end of the thrust-ball plan — for the same 55 mm bore it gives up load to gain OD, height and limiting-speed headroom.
- 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 35 kN never saves a bearing that is running too lightly loaded at 2,800 r/min.
- 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 35/C0a 93 kN ratings and 4.2 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51111; 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 51111?
51111 is a single-direction thrust ball bearing to ISO 104: 55 mm shaft-washer bore, 78 mm outside diameter, 16 mm stack height (2.165 x 3.071 x 0.63 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 35 kN, C0a 93 kN and a 4.2 kN fatigue load limit Pu; the grease limiting speed is 2,800 r/min and the oil rating 4,000 r/min; mass about 226 g.
How is the 51111 designation structured?
511 is the dimension series (light-section 51100 thrust family); 11 encodes the 55 mm bore (bore code x 5). The 78 mm OD and 16 mm height follow the ISO 104 boundary plan for that series.
Can 51111 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 51111?
At the 2,800 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 51111?
The 55/78/16 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 35 kN / C0a 93 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.