51218 bearing: complete specifications & equivalents
The 51218 is a ISO 104 radial bearing sized 90 x 135 x 35 mm (bore x OD x width). Verify dimensions against the official catalog before ordering.
Specification table
| Parameter | Value |
|---|---|
| Brand | NTN |
| Bore diameter d | 90 mm |
| Outer diameter D | 135 mm |
| Width B | 35 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 117 kN |
| Basic static load rating C0 | 325 kN |
| Fatigue load limit Pu | 13.9 kN |
| Limiting speed (mechanical) | 1400 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 1700 g |
| Manufacturer designation | NTN 51218 |
| 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 | 3.543 in |
|---|---|
| Outer diameter D | 5.315 in |
| Width B | 1.378 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 22.5 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) | 19 of 39 |
| Bore above smallest 51200-series size | 80 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51218-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 90×135×35 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 51218 model number is decoded
NTN 51218 belongs to the medium-section 51200 thrust family of single-direction thrust ball bearings: 90 / 135 / 35 mm (shaft bore / OD / height). NTN builds the number from 512 is the dimension series (medium-section 51200 thrust family); 18 encodes the 90 mm bore (bore code x 5). NTN prints 117 kN axial dynamic and 325 kN axial static for this size and a 13.9 kN fatigue load limit Pu. Within the thrust-ball plan, 511 is the light section and 514 the heaviest for a given bore; moving up a series raises the C0a from 325 kN class figures at the cost of OD and height. The shaft washer (bore 90 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
- crusher main-shaft thrust supports
- large rotary-table and index-table thrust rings
- vertical water-pump and turbine thrust blocks
- large crane hook and swivel assemblies
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
- 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
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
Selection pitfalls — read before you substitute
- At 90 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 90 mm bore.
- The 1,400 r/min speed figure assumes the catalogue lubrication state; at high speed the limiting factor is often the minimum load, not the rating table.
- Single-direction means exactly that: thrust on 51218 in the wrong direction separates the washers and drops the ball set — if reversal is possible even during coast-down, engineer against it.
- 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.
- The Ca 117/C0a 325 kN ratings and 13.9 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51218; 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 51218?
51218 is a single-direction thrust ball bearing to ISO 104: 90 mm shaft-washer bore, 135 mm outside diameter, 35 mm stack height (3.543 x 5.315 x 1.378 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 117 kN, C0a 325 kN and a 13.9 kN fatigue load limit Pu; the grease limiting speed is 1,400 r/min and the oil rating 2,000 r/min; mass about 1700 g.
How is the 51218 designation structured?
512 is the dimension series (medium-section 51200 thrust family); 18 encodes the 90 mm bore (bore code x 5). The 135 mm OD and 35 mm height follow the ISO 104 boundary plan for that series.
Can 51218 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 51218?
At the 1,400 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 51218?
The 90/135/35 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 117 kN / C0a 325 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.