Roller chains are widely used in power transmission and conveying systems across packaging, automation, food processing, and other industrial equipment.
Although many roller chains appear similar in size, they are manufactured under different international dimensional standards—most commonly the U.S. ANSI A Series and the European ISO/BS B Series.
Understanding these dimensional differences is essential for correct sprocket matching, stable operation, and longer service life.
Dimensional Differences Between ANSI A Series and ISO B Series
One of the most common misconceptions is that roller chains with the same pitch are interchangeable. However, pitch only defines the distance between adjacent pins and does not guarantee actual compatibility. Other critical dimensions—such as roller diameter, inner width, outer plate height, pin diameter, and overall chain width—vary between standards and directly affect sprocket engagement, load distribution, and wear behavior.
The following sections explain how these dimensional differences are reflected in A Series and B Series roller chain designs.
ANSI A Series
Standard Single-Strand Roller Chain
A Series roller chains are primarily used in the North American market. Their taller link plates result in slightly higher power ratings compared to B Series chains of the same pitch. This design reflects different rating and application priorities rather than overall superiority.
ISO/BS B Series
Standard Single-Strand Roller Chain
B Series roller chains are widely used in Europe and in many global OEM designs. B Series chains typically feature larger pin diameters, providing a greater bearing area than A Series chains of the same pitch. As a result, B Series roller chains generally offer improved wear resistance.
Roller Chain Dimensional Comparison (ANSI vs. ISO/BS)
The table below compares the key dimensions of commonly used roller chain sizes, clearly highlighting the similarities and differences between the standards.
| Chain No. (A Series / B Series) | Pitch (mm (in)) | Roller Diameter (mm) | Width W (mm) | Plate Height (mm) | Pin Diameter (mm) |
|---|---|---|---|---|---|
| #40 / 08B | 12.70 (0.50″) | 7.92 (A Series) vs 8.51 (B Series) | 7.85 (A Series) vs 7.75 (B Series) | 12.07 (A Series) vs 11.8 (B Series) | 3.98 (A Series) vs 4.45 (B Series) |
| #50 / 10B | 15.875 (0.625″) | 10.16 (A Series = B Series) | 9.40 (A Series) vs 9.65 (B Series) | 15.09 (A Series) vs 14.73 (B Series) | 5.09 (A Series) vs 5.08 (B Series) |
| #60 / 12B | 19.05 (0.75″) | 11.91 (A Series) vs 12.07 (B Series) | 12.57 (A Series) vs 11.68 (B Series) | 18.10 (A Series) vs 16.13 (B Series) | 5.96 (A Series) vs 5.72 (B Series) |
| #80 / 16B | 25.40 (1.00″) | 15.88 (A Series = B Series) | 15.75 (A Series) vs 17.02 (B Series) | 24.13 (A Series) vs 21.08 (B Series) | 7.94 (A Series) vs 8.28 (B Series) |
At present, ANSI (ASME) standards specify only the A Series roller chain. In contrast, the BS/ISO 606 roller chain standard has incorporated ANSI A Series roller chains within its scope. As a result, BS/ISO 606 defines both A Series and B Series roller chains in parallel and has become the most widely adopted roller chain standard globally. Other major roller chain standards, such as DIN and JIS, are largely based on BS/ISO 606 and likewise recognize both A Series and B Series roller chains within their specifications.
Conclusion
Even when the pitch is the same, ANSI and BS/ISO B Series roller chains are not interchangeable in practice. Their dimensional differences change how the chain engages with the sprocket.
Installing a different standard on existing sprockets commonly results in abnormal wear, higher noise levels, and a noticeable reduction in service life. Matching the chain and sprocket standard from the outset helps avoid these issues.
