Thrust bearings are specially designed to support axial loads, also called thrust loads, that act parallel to a rotating shaft. They are commonly used in pumps, gearboxes, motors, screw mechanisms, machine tools, and many other types of industrial equipment.
Selecting the correct thrust bearing involves more than matching the shaft diameter. You also need to consider the bearing number, bore diameter, outside diameter, bearing height, axial load capacity, operating speed, load direction, lubrication, and available installation space.
A thrust bearing size chart provides a convenient way to compare common bearing dimensions and identify suitable options. Standard thrust ball-bearing series such as 51100, 51200, 51300, and 51400 cover a wide range of metric shaft sizes and applications.
In this complete guide, you will learn how to read a thrust bearing size chart, understand bearing numbers, compare common thrust bearing types, measure an existing bearing, and select the right size for your application.
What Is a Thrust Bearing?
A thrust bearing is a mechanical bearing designed primarily to support axial forces acting along the axis of a shaft. While radial bearings are mainly designed to handle forces perpendicular to the shaft, thrust bearings are optimized for forces pushing or pulling along the shaft.
A typical thrust ball bearing contains several important components:
- Shaft washer
- Housing washer
- Rolling balls
- Ball cage or separator
- Raceway surfaces
The rolling elements reduce friction between the rotating and stationary components while the washers provide the raceways needed to carry the axial load.
Thrust bearings are especially useful when machinery produces a continuous or intermittent force along the shaft.
Common applications include:
- Pumps
- Electric motors
- Gearboxes
- Machine tools
- Screw jacks
- Compressors
- Fans and blowers
- Automotive equipment
- Marine machinery
- Industrial rotating equipment
The correct thrust bearing depends on the direction and magnitude of the axial force as well as other operating conditions.
Thrust Bearing Size Chart
The following thrust bearing size chart shows common dimensions for metric single-direction thrust ball bearings in the 51100, 51200, 51300, and 51400 families.
Dimensions are shown in millimeters. Always verify the exact dimensions and specifications with the manufacturer’s catalog before purchasing because bearing designs and specifications can vary between manufacturers.
| Bearing Number | Bore d (mm) | Outside Diameter D (mm) | Height H (mm) |
|---|---|---|---|
| 51100 | 10 | 24 | 9 |
| 51200 | 10 | 26 | 11 |
| 51101 | 12 | 26 | 9 |
| 51201 | 12 | 28 | 11 |
| 51102 | 15 | 28 | 9 |
| 51202 | 15 | 32 | 12 |
| 51103 | 17 | 30 | 9 |
| 51203 | 17 | 35 | 12 |
| 51104 | 20 | 35 | 10 |
| 51204 | 20 | 40 | 14 |
| 51105 | 25 | 42 | 11 |
| 51205 | 25 | 47 | 15 |
| 51305 | 25 | 52 | 18 |
| 51405 | 25 | 60 | 24 |
| 51106 | 30 | 47 | 11 |
| 51206 | 30 | 52 | 16 |
| 51306 | 30 | 60 | 21 |
| 51406 | 30 | 70 | 28 |
| 51107 | 35 | 52 | 12 |
| 51207 | 35 | 62 | 18 |
| 51307 | 35 | 68 | 24 |
| 51407 | 35 | 80 | 32 |
| 51108 | 40 | 60 | 13 |
| 51208 | 40 | 68 | 19 |
| 51308 | 40 | 78 | 26 |
| 51408 | 40 | 90 | 33 |
| 51109 | 45 | 65 | 14 |
| 51209 | 45 | 73 | 20 |
| 51309 | 45 | 85 | 28 |
| 51409 | 45 | 100 | 39 |
| 51110 | 50 | 70 | 14 |
| 51210 | 50 | 78 | 22 |
| 51310 | 50 | 95 | 31 |
| 51410 | 50 | 110 | 43 |
| 51111 | 55 | 78 | 16 |
| 51211 | 55 | 90 | 25 |
| 51311 | 55 | 105 | 35 |
| 51411 | 55 | 120 | 48 |
| 51112 | 60 | 85 | 17 |
| 51212 | 60 | 95 | 26 |
| 51312 | 60 | 110 | 35 |
| 51412 | 60 | 130 | 51 |
| 51113 | 65 | 90 | 18 |
| 51213 | 65 | 100 | 27 |
| 51313 | 65 | 115 | 36 |
| 51413 | 65 | 140 | 54 |
| 51114 | 70 | 95 | 18 |
| 51214 | 70 | 105 | 27 |
| 51314 | 70 | 125 | 40 |
| 51414 | 70 | 150 | 60 |
Understanding Thrust Bearing Dimensions
Understanding the dimensions in a thrust bearing size chart is essential when selecting a replacement or designing a new bearing arrangement.
Bore Diameter (d)
The bore diameter is the internal diameter of the bearing. It determines the nominal shaft diameter that the bearing is designed to fit.
For example, a 51205 thrust bearing has a nominal 25 mm bore.
The shaft and bearing fit must be appropriate for the operating conditions. Simply having the same nominal diameter does not guarantee that any bearing will be suitable.
Outside Diameter (D)
The outside diameter represents the largest radial dimension of the bearing.
This dimension is important when determining whether the bearing will fit into the available housing or mounting location.
Bearing Height (H)
Bearing height is the overall axial thickness of the bearing assembly.
It is particularly important when installation space along the shaft is limited.
A bearing with the correct bore may still be unsuitable if its outside diameter or height is too large for the machine.
Thrust Bearing Series Explained
Thrust bearings are available in different dimensional series. The series designation provides a quick indication of the bearing’s overall design and dimensions.
51100 Series
The 51100 series is a compact thrust ball-bearing family designed primarily for axial loads in one direction.
These bearings generally have:
- Small outside diameters
- Low axial heights
- Compact designs
- Metric bore sizes
- Relatively low installation space requirements
For example, a 51105 bearing has a 25 mm bore, 42 mm outside diameter, and 11 mm height.
The compact dimensions make this series useful when installation space is limited.
51200 Series
The 51200 series provides larger outside diameters and heights than corresponding 51100 bearings with the same nominal bore.
Examples include:
- 51200 — 10 × 26 × 11 mm
- 51201 — 12 × 28 × 11 mm
- 51202 — 15 × 32 × 12 mm
- 51205 — 25 × 47 × 15 mm
- 51210 — 50 × 78 × 22 mm
This series is widely used for applications requiring a larger bearing envelope than the compact 51100 series.
51300 Series
The 51300 series generally has a larger cross-sectional design than the smaller thrust ball-bearing series.
Examples include:
- 51305 — 25 × 52 × 18 mm
- 51306 — 30 × 60 × 21 mm
- 51307 — 35 × 68 × 24 mm
- 51310 — 50 × 95 × 31 mm
- 51312 — 60 × 110 × 35 mm
The larger dimensions can provide greater capacity for suitable applications, although actual load ratings must be confirmed from the manufacturer’s specifications.
51400 Series
The 51400 series represents another larger thrust ball-bearing size family.
Examples include:
- 51405 — 25 × 60 × 24 mm
- 51406 — 30 × 70 × 28 mm
- 51407 — 35 × 80 × 32 mm
- 51410 — 50 × 110 × 43 mm
- 51412 — 60 × 130 × 51 mm
- 51414 — 70 × 150 × 60 mm
These bearings require more installation space but may be appropriate where a larger bearing size is needed.
How to Read a Thrust Bearing Number
Thrust bearing numbers provide information about the bearing’s series and size.
Consider the example 51205.
The bearing designation identifies a particular standard thrust ball-bearing configuration. Its common nominal dimensions are:
| Specification | Dimension |
|---|---|
| Bearing number | 51205 |
| Bore | 25 mm |
| Outside diameter | 47 mm |
| Height | 15 mm |
The important point is that the bearing number should not be interpreted as a simple measurement code.
For example, 51105 and 51205 both have a 25 mm bore, but their outside diameters and heights are different.
Therefore, you should always verify the complete bearing designation and dimensions before ordering.
Bearing suffixes can also indicate additional characteristics such as cage construction, precision, clearance, lubrication, or other design details depending on the manufacturer.
How to Measure a Thrust Bearing
If the original bearing number has become unreadable, you can measure the bearing to help identify a replacement.
Measure the Bore
Use a vernier caliper or suitable micrometer to measure the internal opening.
Take the measurement across the center of the bearing and avoid measuring at an angle.
The bore is normally represented by d.
Measure the Outside Diameter
Measure across the widest part of the bearing.
This measurement is identified as D and must fit within the available installation area.
Measure the Height
Place the bearing on a flat surface and measure its overall axial thickness.
This measurement is commonly identified as H.
Check the Bearing Number
Before relying entirely on measurements, inspect the bearing washers for stamped or engraved markings.
A complete designation is usually more reliable than approximate physical measurements because several bearing types can have similar dimensions.
Single-Direction vs Double-Direction Thrust Bearings
The direction of axial loading is one of the most important factors when choosing a thrust bearing.
Single-Direction Thrust Bearing
A single-direction thrust bearing is designed to support axial loads primarily in one direction.
It is suitable when the thrust force consistently acts toward one side.
Typical applications include:
- Vertical shafts
- Pumps
- Screw mechanisms
- Certain gear arrangements
- Low-to-moderate speed machinery
The common 51100 and 51200 thrust ball-bearing families include single-direction designs.
Double-Direction Thrust Bearing
A double-direction thrust bearing can support axial loads in both directions.
This design is useful when the shaft experiences reversing thrust during operation.
Applications may include machinery where:
- Rotation reverses
- Axial forces alternate
- Shaft movement occurs in both directions
- Bidirectional thrust support is required
Selecting between single- and double-direction designs should be based on the actual load pattern of the machine.
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Types of Thrust Bearings
Different thrust bearing designs are available for different load, speed, and application requirements.
Thrust Ball Bearings
Thrust ball bearings use balls positioned between bearing washers.
They are commonly selected for applications where axial loads are present and a relatively compact bearing arrangement is required.
Advantages include:
- Compact construction
- Low friction
- Simple design
- Availability in standardized sizes
- Suitable for many moderate-load applications
Common families include 51100, 51200, 51300, and 51400 series.
Spherical Roller Thrust Bearings
Spherical roller thrust bearings use spherical rollers rather than balls.
They are designed for demanding applications involving substantial axial loads and can accommodate certain combined loading and alignment conditions depending on the specific design.
They are often used in:
- Heavy industrial machinery
- Gearboxes
- Extruders
- Pumps
- Cranes
- Marine equipment
- Heavy-duty rotating machinery
Tapered Roller Bearings
Tapered roller bearings use tapered rollers and are designed to handle both radial and axial loads.
They are particularly useful when significant combined loading occurs.
Typical applications include:
- Automotive wheel assemblies
- Gearboxes
- Industrial machinery
- Heavy-duty shafts
- Rotating equipment
They should not be considered a direct replacement for a thrust ball bearing without checking the complete bearing arrangement.
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How to Select the Correct Thrust Bearing Size
Choosing the correct thrust bearing requires more than finding a bearing with the correct bore.
1. Measure the Shaft Diameter
Start by determining the shaft diameter.
For a 25 mm shaft, several bearing families may have the appropriate nominal bore, including 51105, 51205, 51305, and 51405.
However, these bearings have different outside diameters and heights.
2. Determine the Axial Load
Estimate the axial force acting on the bearing.
The selected bearing must have sufficient load capacity for the actual operating conditions.
Consider both:
- Dynamic axial load
- Static axial load
For critical machinery, use calculated loads rather than rough estimates.
3. Check Radial Loading
Determine whether the bearing will also experience radial forces.
Many standard thrust ball bearings are primarily intended for axial loads. If significant radial loading exists, a different bearing type or a combined bearing arrangement may be necessary.
4. Check Available Space
Measure the available space around the bearing.
Check:
- Maximum outside diameter
- Maximum height
- Housing dimensions
- Shaft shoulder
- Washer seating surface
- Adjacent component clearance
A bearing with greater load capacity may not fit in the available space.
5. Consider Operating Speed
Bearing speed is an important selection factor.
Higher rotational speeds can increase friction, heat generation, and lubrication requirements.
Always compare the intended operating speed with the manufacturer’s reference or limiting speed.
6. Check Temperature
Operating temperature affects lubricant performance and bearing materials.
Applications involving high temperatures may require specially selected bearings and lubricants.
7. Select the Correct Lubrication
Depending on the application, thrust bearings may use:
- Grease lubrication
- Oil lubrication
- Specialized lubricants
The correct lubrication method depends on speed, temperature, load, environment, and bearing design.
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Thrust Bearing vs Radial Bearing
Thrust bearings and radial bearings are designed for different primary load directions.
| Feature | Thrust Bearing | Radial Bearing |
|---|---|---|
| Primary load | Axial | Radial |
| Load direction | Parallel to shaft | Perpendicular to shaft |
| Common design | Washers and rolling elements | Inner and outer rings |
| Main purpose | Support thrust loads | Support radial loads |
| Typical applications | Pumps, jacks, vertical shafts | Motors, wheels, machinery |
| Combined loading | Depends on design | Depends on design |
A standard thrust bearing should not be selected simply because it physically fits a machine.
The bearing must be capable of supporting the forces generated during operation.
Common Thrust Bearing Applications
Thrust bearings are used in many machines where axial forces need to be supported or controlled.
Pumps
Pumps can generate substantial axial forces, particularly in vertical and high-load arrangements.
A properly selected thrust bearing helps maintain the correct axial position of the shaft.
Gearboxes
Helical gears and other gear arrangements can generate axial forces during operation.
The bearing arrangement must account for these forces and their direction.
Screw Jacks
Screw mechanisms can generate high axial forces.
Thrust bearings can support these forces while allowing the screw or shaft to rotate with reduced friction.
Vertical Motors
Vertical motor shafts can place significant axial loads on the bearing arrangement because of the shaft and rotor weight.
A suitable thrust-bearing arrangement can help support this load.
Machine Tools
Machine tools may use thrust bearings to control axial movement and maintain shaft positioning during operation.
Industrial Equipment
Compressors, fans, blowers, presses, conveyors, and other rotating equipment may use thrust bearings when axial forces are present.
Common Thrust Bearing Selection Mistakes
Incorrect bearing selection can result in excessive wear, overheating, vibration, noise, and premature failure.
Avoid these common mistakes:
- Choosing only by shaft diameter
- Ignoring axial load
- Ignoring radial load
- Selecting the wrong load direction
- Exceeding the recommended speed
- Using unsuitable lubrication
- Ignoring operating temperature
- Selecting a bearing that is too large for the housing
- Installing washers incorrectly
- Failing to verify manufacturer specifications
- Assuming all bearings with the same number have identical performance
The bearing dimensions are important, but load ratings and operating conditions are equally important.
Thrust Bearing Maintenance Tips
Proper installation and maintenance can significantly improve bearing service life.
Keep the Bearing Clean
Dust, dirt, metal particles, and moisture can damage bearing raceways and rolling elements.
Keep the bearing and surrounding components clean during installation and maintenance.
Use the Correct Lubricant
Insufficient lubrication can increase friction and temperature.
Excessive or unsuitable lubricant can also create problems, particularly at higher speeds.
Always follow the manufacturer’s recommendations.
Inspect for Damage
During maintenance, inspect for:
- Pitting
- Scoring
- Corrosion
- Discoloration
- Damaged rolling elements
- Damaged cages
- Raceway marks
- Excessive looseness
- Unusual noise
Inspect the Shaft and Housing
Replacing the bearing alone may not solve the problem if the shaft or housing is damaged.
Check mating surfaces, shoulders, seating areas, alignment, and dimensions before installing a new bearing.
Frequently Asked Questions
What is a thrust bearing used for?
A thrust bearing is primarily used to support axial loads acting parallel to a shaft. It helps control shaft movement and reduce friction when machinery produces pushing or pulling forces. Common applications include pumps, gearboxes, screw jacks, vertical motors, machine tools, compressors, and other rotating industrial equipment.
How do I choose the correct thrust bearing size?
Start by measuring the shaft diameter, then determine the axial load and load direction. Check outside diameter, bearing height, radial loading, operating speed, temperature, lubrication, and available space. Finally, compare the complete bearing designation and manufacturer’s specifications before selecting the replacement.
What is the difference between 51105 and 51205?
Both 51105 and 51205 have a 25 mm nominal bore, but their external dimensions differ. A common 51105 measures approximately 25 × 42 × 11 mm, while a 51205 measures approximately 25 × 47 × 15 mm. The appropriate bearing depends on the required capacity and available installation space.
Can a thrust bearing handle radial loads?
Standard thrust ball bearings are primarily designed for axial loads and should not automatically be used where substantial radial loading occurs. Some specialized thrust bearing designs can accommodate combined loads. The bearing manufacturer’s load ratings and application recommendations should always be checked before selection.
How do I identify a thrust bearing without a number?
Measure the bore diameter, outside diameter, and overall height using accurate measuring equipment. Then compare these dimensions with a thrust bearing size chart. Also inspect the bearing washers for partial markings. Because different bearing designs can have similar dimensions, measurements should be confirmed against a manufacturer’s catalog.
Conclusion
A thrust bearing size chart is an excellent starting point when identifying or selecting a thrust bearing, but the correct choice depends on much more than the shaft diameter.
The most important dimensions are bore diameter, outside diameter, and bearing height. Common thrust ball-bearing families such as the 51100, 51200, 51300, and 51400 series provide different dimensional options for applications requiring axial load support.
When selecting a bearing, always consider the shaft size, axial load, load direction, radial load, operating speed, temperature, lubrication, and available installation space.
For replacement applications, measure the existing bearing carefully and verify the bearing number whenever possible. For critical industrial equipment, confirm the complete specifications, load ratings, speed limits, and installation requirements using the manufacturer’s current technical documentation.
Choosing the correct thrust bearing size and design helps provide proper shaft support, reliable operation, reduced friction, and longer bearing service life.
Engineer Hassan is a Mechanical Engineer with 16+ years of hands-on experience in mechanical hardware, fasteners, and workshop tools. He focuses on size selection, thread identification, and measurement, helping users choose the correct components with accuracy and safety.