Use this guide to compare precision ball grades, size capabilities, sphericity, diameter tolerance, lot variation, shipment tolerance, and surface roughness across common industry standards, including ABMA Std-10, ISO 3290, and DIN 5401.
Hartford Technologies manufactures precision balls in a wide range of materials, sizes, and grades for OEMs, engineers, and precision buyers that need tight dimensional control and repeatable production quality.
This page is intended as a technical reference for comparing ball grade requirements. For help selecting the right grade or material for your application, request a quote with your size, material, grade, tolerance, and production requirements.
For the fastest response, include your drawing or specification, required standard, nominal size, material, grade, tolerance requirements, surface finish requirements, expected production volume, and any quality documentation needs.
How Hartford Supports Precision Ball Selection
How to Use This Ball Grade & Tolerance Chart
Ball grade is a measure of precision. In general, lower grade numbers indicate tighter tolerances, better sphericity, smaller diameter variation, and smoother surface finish. For example, a Grade 10 ball is more precise than a Grade 100 ball. Any lower grade will meet the tolerance requirements of all higher grades.
When reviewing the charts below, compare the standard your print or specification calls for:
- ABMA Std-10 — commonly used for precision metal balls in North American bearing and industrial applications.
- ISO 3290 — international rolling bearing ball standard covering dimensions and tolerances.
- DIN 5401 — German/European finished steel ball standard for rolling bearing applications.
Hartford Technologies generally uses the American standard ABMA Std-10, but we can convert to any standard as needed.
The right ball grade depends on the application, material, load, speed, sealing requirements, noise requirements, surface finish needs, and how the ball will be used in the final assembly.
The ABMA Std-10 chart below provides precision ball grade data for sphericity, diameter tolerance per container or lot, diameter tolerance per shipment, and surface roughness.
ABMA Std-10 Precision Ball Grade Chart
| Grade | Sphericity | Dia. Tolerance per Container/Lot | Diameter Tolerance Per Shipment | Surface Roughness, Ra | ||||
|---|---|---|---|---|---|---|---|---|
| Inches | MM | Inches | MM | Inches | MM | µinch | µm | |
| 10 | 0.00001 | 0.0002 | 0.00002 | 0.0005 | ±0.0001 | ±0.00254 | 1 | 0.025 |
| 15 | 0.00001 | 0.0004 | 0.00003 | 0.0007 | ±0.0001 | ±0.00254 | 1 | 0.025 |
| 25 | 0.000025 | 0.0006 | 0.00005 | 0.0013 | ±0.0001 | ±0.00254 | 2 | 0.05 |
| 50 | 0.00005 | 0.0013 | 0.0001 | 0.0025 | ±0.0002 | ±0.0050 | 3 | 0.08 |
| 100 | 0.0001 | 0.0025 | 0.0002 | 0.0050 | ±0.0005 | ±0.0127 | 5 | 0.125 |
| 200 | 0.0002 | 0.0051 | 0.0004 | 0.0102 | ±0.0010 | ±0.0254 | 8 | 0.2 |
| 300 | 0.0003 | 0.0076 | 0.0006 | 0.0152 | ±0.0015 | ±0.0381 | n/a | n/a |
| 500 | 0.0005 | 0.0127 | 0.001 | 0.025 | ±0.002 | ±0.050 | n/a | n/a |
| 1000 | 0.0010 | 0.0254 | 0.002 | 0.051 | ±0.005 | ±0.127 | n/a | n/a |
| 2000 | n/a | n/a | 0.005 | 0.127 | ±0.005 | ±0.127 | n/a | n/a |
| Burnishing | n/a | n/a | n/a | n/a | ±0.005 | ±0.127 | n/a | n/a |
For OEM programs, use the ABMA chart to confirm the grade, diameter tolerance, lot consistency, and surface finish required by the print or application. If you are unsure which grade is appropriate, Hartford can help review the application requirements.
ISO 3290 Precision Ball Grade Chart
ISO 3290 is an international standard for rolling bearing balls. The chart below compares grade, sphericity, variation of ball diameter, variation of ball lot diameter, and surface finish.
| Grade | Sphericity | Variation of Ball Diameter | Variation of Ball Lot Diameter | Surface Finish |
|---|---|---|---|---|
| μ meters | μ meters | μ meters | Ra | |
| 3 | .08 | .08 | .13 | .010 |
| 5 | .13 | .13 | .25 | .014 |
| 10 | .25 | .25 | .5 | .020 |
| 16 | .4 | .4 | .8 | .025 |
| 20 | .5 | .5 | 1 | .032 |
| 24 | .6 | .6 | 1.2 | .040 |
| 28 | .7 | .7 | 1.4 | .050 |
| 40 | 1 | 1 | 2 | .060 |
| 60 | 1.5 | 1.5 | 3 | .080 |
| 100 | 2.5 | 2.5 | 5 | .100 |
| 200 | 5 | 5 | 10 | .150 |
ISO 3290 is often used when specifications need to align with international bearing ball standards. Confirm whether your print requires ISO, ABMA, DIN, or a customer-specific tolerance requirement before ordering.
DIN 5401 Precision Ball Grade Chart
DIN 5401 covers finished steel balls for rolling bearing applications. The chart below compares grade, sphericity, variation of ball diameter, variation of ball lot diameter, and surface roughness.
| Grade | Sphericity | Variation of Ball Diameter | Variation of Ball Lot Diameter | Surface Roughness |
|---|---|---|---|---|
| μ meters | μ meters | μ meters | Ra | |
| 3 | .08 | .08 | .13 | .010 |
| 5 | .13 | .13 | .25 | .014 |
| 10 | .25 | .25 | .5 | .020 |
| 16 | .4 | .4 | .8 | .025 |
| 20 | .5 | .5 | 1 | .032 |
| 28 | .7 | .7 | 1.4 | .040 |
| 40 | 1 | 1 | 2 | .050 |
| 100 | 2.5 | 2.5 | 5 | .060 |
| 200 | 5 | 5 | 10 | .080 |
| 500 | 25 | 25 | n/a | n/a |
DIN 5401 may be referenced in European or international bearing applications. Hartford can help compare DIN requirements with ABMA or ISO specifications when reviewing an RFQ.
Ball Capability: Size, Grade & Material
Hartford manufactures precision balls in multiple materials, sizes, and standard grade ranges. The table below shows standard size and grade capabilities by material.
Use this table to compare available material families, smallest and largest standard sizes, and typical best/least standard grades.
| Material | Smallest Standard Size | Smallest Standard Size | Largest Standard Size | Largest Standard Size | Best Standard Grade | Least Standard Grade | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Stainless Steels | |||||||||||
| 302/304 | 1.5mm | 1/16″ | 50.8mm | 2″ | 50 | 1000 | |||||
| 316 | 1.5mm | 1/16″ | 50.8mm | 2″ | 50 | 1000 | |||||
| 420 | 1.5mm | 1/16″ | 50.8mm | 2″ | 25 | 1000 | |||||
| 430 | 1.5mm | 1/16″ | 50.8mm | 2″ | 100 | 1000 | |||||
| 440c | 1mm | 1/32″ | 50.8mm | 2″ | 10 | 1000 | |||||
| CorrTech Steel | 1mm | 1/32″ | 50.8mm | 2″ | 10 | 1000 | |||||
| Other Materials | |||||||||||
| Chrome | 1mm | 1/32″ | 50.8mm | 2″ | 10 | 1000 | |||||
| Low Carbon | 1mm | 1/32″ | 50.8mm | 2″ | 100 | 1000 | |||||
| Brass | 1.5mm | 1/16″ | 25.4mm | 1″ | 200 | 1000 | |||||
| Tungsten Carbide | 1.5mm | 1/16″ | 50.8mm | 2″ | 10 | 100 | |||||
| Borosilicate Glass | 2mm | 3/32″ | 31.75mm | 1.25″ | 100 | 1000 | |||||
| Soda Lime Glass | 2mm | 3/32″ | 31.75mm | 1.25″ | 100 | 1000 | |||||
| Plastic | |||||||||||
| Acetal (Delrin and Celcon) | 1.5mm | 1/16″ | 25.4mm | 1″ | G0 | G3 | |||||
| Nylon | 1.5mm | 1/16″ | 25.4mm | 1″ | G0 | G3 | |||||
| Polyethylene | 1.5mm | 1/16″ | 25.4mm | 1″ | G0 | G3 | |||||
| Polypropylene | 1.5mm | 1/16″ | 25.4mm | 1″ | G0 | G3 | |||||
| PTFE (Teflon) | 1.5mm | 1/16″ | 25.4mm | 1″ | G0 | G3 | |||||
Material-specific precision ball pages
For more detail by material, visit:
Need Help Choosing the Right Precision Ball Grade?
Hartford can help review your application, material requirements, ball size, grade, tolerance, surface finish, and production needs.
For the fastest response, include your drawing or specification, required standard, nominal size, material, grade, tolerance requirements, surface finish requirements, expected production volume, and any quality documentation needs.
How Hartford Supports Precision Ball Selection
Selecting the right ball grade is not only about choosing the tightest tolerance. A higher-precision grade may be necessary for demanding bearing, valve, medical, instrumentation, or mechanical applications, but the best choice depends on the application requirements and production environment.
Hartford Technologies supports OEMs and precision buyers with:
- Ball material selection
- Grade and tolerance review
- Size and diameter capability review
- Surface finish considerations
- Application-specific recommendations
- Production-volume manufacturing support
- Quality documentation and traceability
- US engineering support and global manufacturing flexibility
Hartford manufactures precision balls, bearing components, custom bearing assemblies, precision pins, and custom precision rollers for OEMs and Tier suppliers that need tight tolerances and repeatable production quality.
Key Ball Grade & Tolerance Definitions
Ball Grade
Ball grade defines the precision level of a ball. It is based on factors such as sphericity, diameter variation, lot variation, and surface roughness. Lower grade numbers generally mean tighter tolerances and higher precision.
Sphericity
Sphericity measures how close the ball is to a perfect sphere. A tighter sphericity value means the ball has less deviation from a true round shape.
Diameter Tolerance
Diameter tolerance defines the acceptable variation from the specified nominal ball diameter. This matters when the ball must fit into a precise bearing, valve, or mechanical assembly.
Variation of Ball Diameter
Variation of ball diameter measures the difference between the largest and smallest diameter readings on an individual ball.
Variation of Ball Lot Diameter
Variation of ball lot diameter measures the allowable difference across a group, lot, shipment, or container of balls. This is important when consistency across production quantities matters.
Diameter Tolerance Per Shipment
Diameter tolerance per shipment defines the allowable diameter range across a shipment of different lots, helping buyers understand the allowable tolerance control consistency between received lots.
Surface Roughness / Ra
Surface roughness, often shown as Ra, measures the texture of the ball surface. A smoother surface can be important for bearing performance, sealing, noise, wear, and rolling consistency.
What to Include in a Precision Ball RFQ
To help Hartford evaluate your precision ball requirements, include as much of the following information as possible:
- Ball material
- Nominal diameter
- Required grade
- Applicable standard: ABMA, ISO, DIN, or customer-specific
- Sphericity requirement
- Diameter tolerance requirement
- Lot or shipment tolerance requirement
- Surface roughness / Ra requirement
- Application or assembly type
- Operating environment
- Annual production volume
- Prototype or production timeline
- Required quality documentation or certifications
- Drawing, print, or specification if available
Hartford’s team can review your requirements and recommend the best path for your precision ball application.
Frequently Asked Questions About Ball Grades and Tolerances
What does ball grade mean?
Ball grade defines the precision level of a ball. It typically accounts for sphericity, diameter variation, lot variation, and surface roughness. Lower grade numbers generally indicate tighter tolerances and higher precision.
Is a lower ball grade more precise?
Yes. In most precision ball standards, lower grade numbers indicate tighter tolerances. For example, a Grade 10 ball is more precise than a Grade 100 ball.
What is the difference between Grade 10,Grade 100, and Grade 1000 balls?
Grade 10 balls have tighter sphericity, diameter variation, and surface finish requirements than Grade 100 or Grade 1000 balls. Grade 10 is typically used where higher precision is required, while Grade 100 may be suitable for less demanding applications. Grade 1,000 is often used in applications where high precision is not required.
What is ABMA Std-10?
ABMA Std-10 is a ball standard used to define precision requirements for metal balls, including sphericity, diameter tolerance, lot variation, shipment tolerance, and surface roughness. This was published by the American Bearing Manufacturers Association and has become the industry standard for measuring most balls.
What is ISO 3290?
ISO 3290 is an international standard for rolling bearing balls. It defines precision requirements such as sphericity, variation of ball diameter, variation of ball lot diameter, and surface finish.
What is DIN 5401?
DIN 5401 is a standard for finished steel balls used in rolling bearing applications. It includes grade, sphericity, variation of ball diameter, variation of ball lot diameter, and surface roughness requirements.
What does sphericity mean for precision balls?
Sphericity measures how close a ball is to a perfect sphere. Tighter sphericity helps support more consistent rolling, sealing, and fit in precision applications.
What does surface roughness Ra mean?
Surface roughness Ra measures the average texture of a surface. For precision balls, a smoother surface may be important for bearing performance, sealing, wear resistance, noise control, and rolling consistency.
How do I choose the right precision ball grade?
Start with the application requirements, material, nominal size, load, speed, surface finish needs, and applicable standard. If the print specifies ABMA, ISO, DIN, or customer-specific tolerances, use that requirement first. Hartford can help review the application and recommend an appropriate ball grade.
Does Hartford manufacture precision balls to ABMA, ISO, or DIN standards?
Hartford manufactures precision balls across multiple materials and grade ranges and provides reference charts for ABMA Std-10, ISO 3290, and DIN 5401. The exact grade and standard should be confirmed during the RFQ process based on the application and drawing requirements.
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