In industries such as machinery manufacturing, bearings, valves, medical devices, and aerospace, the precision grade of steel balls is one of the most critical factors affecting performance and service life. Terms like G10, G20, G40, and G100 appear frequently, yet many buyers are not fully aware of what these grades mean.

This article provides a clear and comprehensive explanation of steel ball precision grades, helping you make better purchasing decisions and select the right specifications for different applications.

1. Origins of Steel Ball Precision Grades: ISO & AFBMA Standards

Globally, steel ball accuracy is primarily defined by two standards:

● ISO 3290 International Standard

The most widely used classification system, specifying:

• Geometric accuracy

• Diameter variation

• Surface roughness

• Batch consistency

Common grades such as G10, G20, G40, G100 originate from ISO 3290 (latest version ISO 3290-1).

● AFBMA (ANSI) Standard

Used mainly in North America, with grades corresponding to ISO values using numbers like 10, 24, 48, etc.

2. What Are G10 and G20? Understanding Precision Grades

The smaller the grade number, the higher the precision.

Summary: G10 has roughly double the precision of G20, while G20 is significantly more accurate than G40 and G100.

3. How Are Precision Grades Determined? Four Key Technical Indicators

Steel ball accuracy is not defined by a single measurement but by a combination of four major factors:

1. Sphericity (Roundness)

Measures how close the ball is to a perfect sphere.
Higher sphericity = smoother rotation and lower vibration.

2. Diameter Variation

Consistency of diameter within a batch.
Low variation ensures easier assembly and more stable performance.

3. Surface Roughness

The smoother the surface, the less friction and wear during operation.
G10 typically achieves a near-mirror finish.

4. Hardness & Material Consistency

High precision requires stable hardness and high-quality materials such as stainless steel, bearing steel, carbon steel, etc.

4. Typical Applications of Different Precision Grades

● G10 – Ultra-High Precision

✔ Aerospace instruments
✔ High-speed spindle systems
✔ High-end medical devices
✔ Applications with strict noise requirements (e.g., brushless motors)

● G20 – High Precision

✔ Medium to high-speed bearings
✔ Automotive components
✔ Stable mechanical equipment

● G40–G100 – Medium Precision

✔ Industrial machinery
✔ Power tools
✔ Valve mechanisms

● G200 – General Industrial Use

✔ Low-speed machinery
✔ General transmission parts

5. How to Choose the Right Precision Grade? (Purchasing Tips)

Here is a quick guide for buyers:

If you're unsure which grade is suitable, simply tell us your application scenario—we will recommend the most suitable material and precision grade.

6. What We Offer as a Professional B2B Steel Ball Manufacturer & Trader

As a B2B integrated manufacturer and trading supplier of industrial balls, we provide:

● Complete Range of Materials

Stainless steel (304/316/420/440C), bearing steel (GCr15), carbon steel, aluminum balls, copper/brass balls, plastic balls, and more.

● Precision Grades Covering G10–G1000

Meeting demands from high-end precision applications to standard industrial usage.

● Automated Inspection Systems

Ensuring:

• Diameter consistency

• Roundness accuracy

• Surface defect detection

• Batch stability

● OEM/ODM and Packaging Customization

Perfect for brand owners, distributors, and large-scale manufacturers.