Buyers often assume that “1/2 inch chain” means the same thing everywhere. It does not. ANSI A-series and ISO/BS/DIN B-series chains share pitch sizes but differ in roller diameter and inner width – a B-series chain will not run correctly on an A-series sprocket, even when the pitch matches.
The two families
| A-series (ANSI) | B-series (ISO / BS / DIN) | |
|---|---|---|
| Standard | ASME B29.1 | ISO 606-B / BS 228 / DIN 8187 |
| Common markets | USA, Canada, Japan, Latin America | Europe, UK, Middle East, Commonwealth |
| Numbering | 25, 35, 40, 50, 60, 80… | 04B, 06B, 08B, 10B, 12B, 16B… |
| Link plates | Usually figure-8 profile | Usually straight (flat) side plates |
Why the same pitch is not the same chain
Take the 1/2″ pitch chains as an example:
| Dimension | 08B-1 (B-series) | 08A-1 / ANSI 40 (A-series) |
|---|---|---|
| Pitch | 12.700 mm | 12.700 mm |
| Roller diameter | 8.51 mm | 7.95 mm |
| Inner width | 7.75 mm | 7.85 mm |
| Pin diameter | 4.45 mm | 3.96 mm |
The roller is 0.56 mm larger on the B-series chain. That is enough to change how the chain sits in the sprocket pocket – which is why “it looks the same” is not a safe assumption when replacing a chain.
How to tell which family you have
- Read the stamping on the side plate: 08B-1, 16B-2, 50-1, 80-1 and so on. Numbers with a letter (08B, 10B, 16B) are B-series; plain numbers (40, 50, 60, 80) are ANSI.
- Measure the roller diameter with a caliper and compare it with a standard table.
- Check the side plate profile – straight plates are typical of B-series, figure-8 of A-series.
- When in doubt, measure the sprocket: the tooth gap and roller seat are cut for one family only.
Practical advice for buyers
- Specify the standard, not just the pitch, on your purchase order: “16B-1 to ISO 606-B” leaves no room for misinterpretation.
- Replacing a chain on imported European machinery? It is almost always B-series.
- Machine built in the USA or for the American market? It is almost always A-series.
- Keep chain and sprockets as a matched set – mixing families wears both out quickly.
UIB manufactures both families
UIB supplies A-series (ANSI) and B-series (ISO / BS / DIN) roller chains in carbon steel and stainless steel SUS304, in simplex, duplex and triplex construction, with attachments and cut-to-length service – plus matched sprockets, so you can order the complete drive from one supplier.
Send us your chain number for a quotation.
