Converting between ANSI and ISO roller chain specifications is a common requirement for Australian engineers and procurement teams who source chain from multiple countries or work with equipment designed to one standard and must source replacement chain from suppliers working to the other. While ANSI and ISO roller chain standards share the same fundamental design, they differ in specific dimensions — most critically the roller diameter — in ways that make some ANSI and ISO chains of the same pitch non-interchangeable on the same sprocket.
The Fundamental Issue: Same Pitch, Different Roller Diameter
The most important difference between ANSI B29.1 and ISO 606 roller chain at the same nominal pitch is the roller diameter. For most common sizes, the ISO B-series chain has a larger roller than the ANSI chain of nominally the same pitch. This larger roller does not seat correctly in an ANSI sprocket — the roller is too large to remove to the tooth root, causing elevated engagement and rapid wear.
| ANSI Chain | ISO/BS Equivalent | Pitch (mm) | ANSI Roller OD (mm) | ISO B-Series Roller OD (mm) | Interchangeable on Same Sprocket? |
|---|---|---|---|---|---|
| ANSI 35 | 06B (BS/ISO B) | 9.525 | 5.08 | 6.35 | NO — ISO roller 25% larger; sprockets not interchangeable |
| ANSI 40 | 08A (ISO A) | 12.70 | 7.92 | 7.92 | Yes — ISO 08A and ANSI 40 have the same roller diameter |
| ANSI 40 | 08B (BS/ISO B) | 12.70 | 7.92 | 8.51 | NO — ISO 08B has a larger roller than ANSI 40 sprocket can accommodate |
| ANSI 50 | 10A (ISO A) | 15.875 | 10.16 | 10.16 | Yes — ISO 10A and ANSI 50 have the same roller diameter |
| ANSI 60 | 12A (ISO A) | 19.05 | 11.91 | 11.91 | Yes — ISO 12A and ANSI 60 have the same roller diameter |
| ANSI 60 | 12B (BS/ISO B) | 19.05 | 11.91 | 15.88 | NO — ISO 12B roller is 33% larger; sprockets not interchangeable |
| ANSI 80 | 16A (ISO A) | 25.40 | 15.88 | 15.88 | Yes — ISO 16A and ANSI 80 have the same roller diameter |
| ANSI 80 | 16B (BS/ISO B) | 25.40 | 15.88 | 19.05 | NO — ISO 16B roller is 20% larger; sprockets not interchangeable |
The ISO 606 A-Series vs B-Series Distinction
There are two distinct non-ANSI standards frequently confused in conversion discussions: ISO 606 A-series (American-derived) and ISO 606 B-series (derived from British Standard BS 228). The ISO A-series chain (ISO 08A, 10A, 12A, 16A etc.) has the same dimensions as ANSI chain at each pitch — these are fully interchangeable with ANSI chain and ANSI sprockets. The ISO B-series chain (ISO 06B, 08B, 12B, 16B etc.) has different roller diameters and inner widths from the equivalent ANSI chain — these require B-series sprockets and are not interchangeable with ANSI chain on the same sprocket.
How to Find the ISO Equivalent for an ANSI Chain
| ANSI Designation | ISO A-Series (ANSI-compatible) | ISO B-Series (BS-derived) | Conversion Note |
|---|---|---|---|
| ANSI 40 | 08A | 08B | 08A is fully interchangeable with ANSI 40; 08B has larger roller — do not mix with ANSI 40 sprockets |
| ANSI 50 | 10A | 10B | 10A is fully interchangeable with ANSI 50; verify inner width before mixing 10B |
| ANSI 60 | 12A | 12B | 12A is fully interchangeable with ANSI 60; 12B has much larger roller — not interchangeable with ANSI 60 sprockets |
| ANSI 80 | 16A | 16B | 16A is fully interchangeable with ANSI 80; 16B has larger roller — not interchangeable with ANSI 80 sprockets |
| ANSI 100 | 20A | 20B | 20A is fully interchangeable with ANSI 100; verify roller diameter before mixing 20B |
| ANSI 120 | 24A | 24B | 24A is fully interchangeable with ANSI 120; verify roller diameter before mixing 24B |
Practical Conversion Procedure
Determine the ANSI chain number from equipment documentation, the chain label, or by measuring the pitch and roller dimensions.
Use the table above: ANSI 40 = ISO 08A; ANSI 60 = ISO 12A; ANSI 80 = ISO 16A.
Verify the roller diameter on the ISO chain specification sheet matches the ANSI chain roller diameter. For ISO A-series chains, it should match exactly.
The ISO chain inner width must be larger than the sprocket tooth width for the chain to fit over the tooth.
If all dimensions are verified compatible, the ISO chain can be installed on the ANSI sprocket without modification. Document the specification conversion for future maintenance reference.
EverPower Roller Chains Australia can advise on ANSI and ISO roller chain equivalence and supply the correct chain specification for Australian equipment using either standard. Contact +61 2 9708 3322 or [email protected].
+61 2 9708 3322 | [email protected] | 27 Harley Crescent, Condell Park NSW 2201