51215 bearing: complete specifications & equivalents
The 51215 is a ISO 104 radial bearing sized 75 x 110 x 27 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 | 110 mm |
| Width B | 27 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 77.5 kN |
| Basic static load rating C0 | 209 kN |
| Fatigue load limit Pu | 9.4 kN |
| Limiting speed (mechanical) | 1800 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 874 g |
| Manufacturer designation | NTN 51215 |
| 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 & 51200-series range
| Bore d | 2.953 in |
|---|---|
| Outer diameter D | 4.331 in |
| Width B | 1.063 in |
| ISO bore code | 15 |
| Radial section height (D−d)/2 | 17.5 mm |
| Smallest bore in 51200-series | 10 mm |
| Largest outer diameter in 51200-series | 520 mm |
| Width range across 51200-series | 11–112 mm |
| Bore position in 51200-series (smallest first) | 16 of 39 |
| Bore above smallest 51200-series size | 65 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51215-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 75×110×27 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 51215 model number is decoded
From the medium-section 51200 thrust family, 51215 measures 75 mm through the shaft washer, 110 mm over the outside and 27 mm in assembled height. Reading the code: 512 is the dimension series (medium-section 51200 thrust family), and 15 encodes the 75 mm bore (bore code x 5). On speed, the grease limiting speed is 1,800 r/min and the oil rating 2,600 r/min. Against a thrust roller bearing of the same 75 mm bore, this bearing is cheaper, quieter and happier at speed, but carries far less load per mm of section. 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
- large rotary-table and index-table thrust rings
- vertical water-pump and turbine thrust blocks
- large crane hook and swivel assemblies
- rolling-mill screwdown and adjustment screws
Known failure patterns
- cage pocket wear and ball skid polish after long running below the minimum axial load, the balls sliding instead of rolling on the washers
- housing-washer rocking on an out-of-square support face, seen as uneven wear around the raceway circle and rising running torque
- 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
- edge loading from a shaft washer mounted off-centre, cutting the contact ellipse short at one side of the track
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 512 medium section is the default choice: balanced height and capacity for general vertical-shaft duty at 75 mm bore.
- Below the minimum axial load the balls skid; the catalogue Ca of 77.5 kN never saves a bearing that is running too lightly loaded at 1,800 r/min.
- The 1,800 r/min speed figure assumes the catalogue lubrication state; at high speed the limiting factor is often the minimum load, not the rating table.
- 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 77.5/C0a 209 kN ratings and 9.4 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51215; 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 51215?
51215 is a single-direction thrust ball bearing to ISO 104: 75 mm shaft-washer bore, 110 mm outside diameter, 27 mm stack height (2.953 x 4.331 x 1.063 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 77.5 kN, C0a 209 kN and a 9.4 kN fatigue load limit Pu; the grease limiting speed is 1,800 r/min and the oil rating 2,600 r/min; mass about 874 g.
How is the 51215 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 15 encodes the 75 mm bore (bore code x 5). The 110 mm OD and 27 mm height follow the ISO 104 boundary plan for that series.
Can 51215 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 51215?
At the 1,800 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 51215?
The 75/110/27 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 77.5 kN / C0a 209 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.