51318 bearing: complete specifications & equivalents
The 51318 is a ISO 104 radial bearing sized 90 x 155 x 50 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 | 155 mm |
| Width B | 50 mm |
| Material | GCr15 |
| Seal / shield | open |
| Internal clearance | CN |
| Tolerance class | P0 |
| Basic dynamic load rating C | 213 kN |
| Basic static load rating C0 | 525 kN |
| Fatigue load limit Pu | 21.3 kN |
| Limiting speed (mechanical) | 1100 rpm |
| Operating temperature | -40 to +120 °C |
| Mass | 3740 g |
| Manufacturer designation | NTN 51318 |
| 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 & 51300-series range
| Bore d | 3.543 in |
|---|---|
| Outer diameter D | 6.102 in |
| Width B | 1.969 in |
| ISO bore code | 18 |
| Radial section height (D−d)/2 | 32.5 mm |
| Smallest bore in 51300-series | 25 mm |
| Largest outer diameter in 51300-series | 340 mm |
| Width range across 51300-series | 18–110 mm |
| Bore position in 51300-series (smallest first) | 14 of 25 |
| Bore above smallest 51300-series size | 65 mm |
Cross references & equivalents
| Equivalent model | Brand | Match level | Note |
|---|---|---|---|
| 51318-SKF | SKF | partial Main dimensions match; tolerances, seals or internal clearance differ. | Same 90×155×50 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 51318 model number is decoded
At 90 x 155 x 50 mm, NTN 51318 sits in the heavy-section 51300 thrust family of the single-direction thrust programme. Decoding 51318: 513 is the dimension series (heavy-section 51300 thrust family), with 18 encodes the 90 mm bore (bore code x 5). The washer section here is 32.5 mm of radial height, and the catalogue couples it with Ca 213 kN / C0a 525 kN. If the duty is high speed with light thrust, check the minimum axial load formula first; a too-large thrust ball bearing fails by skid long before its Ca of 213 kN is ever approached. 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
- ship winch and capstan thrust shafts
- crusher main-shaft thrust supports
- large rotary-table and index-table thrust rings
- vertical water-pump and turbine thrust blocks
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
- lubricant starvation scoring on the raceway track when grease is thrown outward by centrifugal effect and never replaced
- washer face corrosion under long standstill in humid service, later printed into the raceway as evenly spaced pitting
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 513 heavy section buys capacity with a larger 155 mm OD and taller stack — check the housing space before upgrading a 512 position to this series.
- A housing washer pressed tight in its seat cannot self-centre; the resulting eccentric running shows up as cage wear long before raceway fatigue.
- Radial load is the silent killer here: a belt pull or gear force on the same shaft must land on a radial bearing, because 51318 has no radial capacity at all.
- The C0a of 525 kN is a static rating: sizing continuous working thrust from C0a alone overstates what the raceway survives.
- The Ca 213/C0a 525 kN ratings and 21.3 kN Pu here are NTN Ball and Roller Bearings CAT.No.2203E figures for 51318; 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 51318?
51318 is a single-direction thrust ball bearing to ISO 104: 90 mm shaft-washer bore, 155 mm outside diameter, 50 mm stack height (3.543 x 6.102 x 1.969 in). From NTN Ball and Roller Bearings CAT.No.2203E: axial Ca 213 kN, C0a 525 kN and a 21.3 kN fatigue load limit Pu; the grease limiting speed is 1,100 r/min and the oil rating 1,600 r/min; mass about 3740 g.
How is the 51318 designation structured?
513 is the dimension series (heavy-section 51300 thrust family); 18 encodes the 90 mm bore (bore code x 5). The 155 mm OD and 50 mm height follow the ISO 104 boundary plan for that series.
Can 51318 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 51318?
At the 1,100 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 51318?
The 90/155/50 mm envelope is ISO 104 interchangeable, but washer bore codes, raceway osculation and ratings are maker-specific. Re-verify Ca 213 kN / C0a 525 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.