What Is the Difference Between BS and ISO Roller Chain Standards

For engineers and procurement teams in Australia who work with British-designed equipment, older Australian plant from the 1970s to 1990s, or international supply chains, understanding the relationship between BS roller chain standards (British Standard) and ISO (International Organisation for Standardisation) chain specifications is essential for specifying correct replacement chain.

BS versus ISO roller chain standard comparison showing B-series and A-series designation systems

The Historical Background: BS 228 and ISO 606

British Standard BS 228 was the foundational specification for short-pitch precision roller chain used in British and British-influenced countries (including Australia) from the mid-20th century onward. BS 228 defined what became known as “BS chain” or “B-series chain” — characterised by larger rollers and wider inner plates than the American ANSI chain of the same pitch. In 1994, ISO 606 was published and incorporated both the ANSI-derived dimensions (as the ISO “A-series”) and the BS-derived dimensions (as the ISO “B-series”) into a single international standard. BS 228 was then withdrawn and replaced by ISO 606, but B-series chain remains in production and use globally.

Current Standard Designations: What ISO 606 Contains

Series	Designation Format	Example	Origin	ANSI Compatible?
A-series (ISO standard)	Number followed by A: 08A, 10A, 12A, 16A	ISO 08A = pitch 12.70 mm, roller 7.92 mm	Derived from ANSI dimensions	Yes — A-series chains have same dimensions as ANSI chain of same pitch
B-series (BS-derived)	Number followed by B: 06B, 08B, 10B, 12B, 16B	ISO 08B = pitch 12.70 mm, roller 8.51 mm	Derived from original BS 228 dimensions	No — B-series roller is larger than ANSI sprocket can accommodate

Specific Dimensional Differences Between B-Series and ANSI Chain

Pitch	ANSI Designation	ISO B-Series	ANSI Roller OD (mm)	ISO B Roller OD (mm)	Difference
9.525 mm	ANSI 35	06B	5.08	6.35	+25%
12.70 mm	ANSI 40	08B	7.92	8.51	+7%
15.875 mm	ANSI 50	10B	10.16	10.16	No difference at this size
19.05 mm	ANSI 60	12B	11.91	15.88	+33%
25.40 mm	ANSI 80	16B	15.88	19.05	+20%
31.75 mm	ANSI 100	20B	19.05	25.40	+33%

Dimensional table comparing BS 228 B-series roller diameters versus ANSI B29.1 roller diameters at each pitch

Which Standard Is Used in Australia?

Australia historically sourced much of its industrial chain from British manufacturers, and older Australian plant and equipment from the 1960s through the 1990s commonly uses BS-dimensioned chain and sprockets. Modern Australian equipment and chain procurement increasingly uses ANSI-dimensioned chain, particularly for Chinese-manufactured chain which is predominantly produced to ANSI B29.1. When replacing chain on older Australian equipment, always verify whether the original chain was B-series (BS) or A-series (ANSI-equivalent) before ordering, as the sprockets are different between the two standards at most pitch sizes.

How to Identify Whether Existing Chain Is B-Series or A-Series

The most reliable method is to measure the roller diameter with a vernier caliper and compare to the expected values for A-series (ANSI) and B-series at the measured pitch. For example: an 08B chain has an 8.51 mm roller; an ANSI 40 at the same pitch has a 7.92 mm roller. A measurement of 8.51 mm verifies B-series. A measurement of 7.92 mm verifies A-series/ANSI. The difference (0.59 mm) is well within the measurement accuracy of a vernier caliper.

EverPower Roller Chains Australia stocks both ANSI roller chain and ISO B-series (BS) roller chain for equipment requiring either standard, with matching sprockets in both specifications. Contact +61 2 9708 3322 or [email protected].

+61 2 9708 3322 | [email protected] | 27 Harley Crescent, Condell Park NSW 2201

Frequently Asked Questions

My equipment manual says “BS chain” — does this mean BS 228 or ISO 606? +

In practice, “BS chain” in an equipment manual almost always refers to B-series (British Standard-derived) chain as defined in BS 228, now incorporated into ISO 606 as the B-series. The correct replacement chain is ISO B-series at the specified pitch (for example 12B if the pitch is 19.05 mm).

Can I replace BS chain with ISO chain? +

If you replace BS chain (B-series, larger roller) with ISO 606 A-series chain (ANSI-equivalent, smaller roller) of the same pitch, the A-series chain has a smaller roller that can theoretically run on a B-series sprocket — the smaller roller has clearance in the larger gullet. For best results, keep chain and sprocket to the same series. If converting from B-series to A-series, replace both chain AND sprockets simultaneously.

I need to order 12B chain in Australia — is this easy to source? +

12B chain is less commonly stocked than ANSI 60 in Australia, but specialist chain suppliers maintain stock. Contact EverPower Roller Chains Australia — we maintain stock of B-series chain for older Australian equipment requiring the BS specification.

Are the breaking loads the same for A-series and B-series chain at the same pitch? +

No — ISO B-series chain at most pitches has a higher minimum tensile strength than ANSI chain of the same pitch, because the B-series chain has a larger roller and in many cases a wider plate, increasing the cross-sectional area and load capacity. For example, ISO 12B has a minimum tensile strength of approximately 28.9 kN, while ANSI 60 at the same pitch has 21.8 kN.

Does the ISO 606 standard apply globally — can I specify ISO 606 to any chain manufacturer? +

ISO 606 is adopted internationally by most major chain manufacturing countries including China, Japan, Germany, and the UK. Specifying ISO 606 to a Chinese chain manufacturer will typically be interpreted as A-series (ANSI-equivalent) chain unless the B-series is explicitly specified. If you require B-series chain, specify the B-series designation explicitly (for example “12B per ISO 606 B-series”).