Identify roller chain FB Chain Knowledge Hub

How to quickly and easily identify roller chain

I carry around a large number of chain catalogues to help with roller chain identification when I am working at customers’ sites. At first, glance, trying to identify a roller chain can seem very confusing with catalogues featuring lots of special attachments and extended pins, but in fact, the vast majority of roller chain is based on just two main standards:

  • ASME B29.1 – 2011 Precision Power Transmission Roller Chains, Attachments, and Sprockets – often referred to as ANSI or American standard chain
  • ISO 606:2015 Short-pitch transmission precision roller and bush chains, attachments and associated chain sprockets – often referred to as BS or European standard.

The three key dimensions needed to identify roller chain – according to both ISO & ANSI standards – are chain pitch, roller diameter and the inner width of the roller link.

Full dimensions of every roller chain can be found using our Roller Chain Quick Find page.

It’s rare to see the key dimensions of both standards of roller chain displayed together in a chain manufacturer’s catalogue as they are generally laid out for people designing new equipment and not for maintenance technicians.

Roller chains from the two different chain standards have very similar sizes so it can be easy to identify the wrong chain if you’re only looking at a table with one type of chain in it.

Roller Chain Size Chart

I keep this little roller chain identification table with me showing the key dimensions to save me flicking through the catalogue, which is handy when I am on site.

PitchSeriesMin. Inner WidthMax. Roller DiameterMax Bearing Pin Diameter
31.751 1/4″20B-1100-119.5618.9019.0519.0510.199.54
38.101 1/2″24B-1120-125.4025.2225.4022.2314.6311.11
44.451 3/4″28B-1140-130.9925.2227.9425.4015.9012.71
63.502 1/2″40B-1200-138.1037.8539.3739.6822.8919.85

One of the hardest dimensions to determine is the chain pitch, as keeping a rule or Vernier steady on the pin centres while leaning into a machine is not easy. If I have any doubts, then I do the following: measure across the outside of two consecutive rollers using Vernier callipers, then measure the roller diameter and subtract one roller diameter to obtain the correct pitch.

In most case the roller chain type is often stamped on the outer link plate; for example, 50 if ANSI or 10B if BS size. The first digits refer to the pitch of the chain and vary according to the series.

ANSI series chain is measured in 8ths of an inch – but only the numerator of the fraction is given. For example, 4 represents 4/8″ – which can be reduced to ½” chain – and would be stamped 40.

BS series chain is measured in 16ths of an inch so 8/16″ is reduced to ½”, and the chain would be stamped 08B.

Selecting the wrong roller chain can cause major problems as it will not engage the sprocket correctly and they have different capacities, so you could get a premature failure or a shorter operating life.

Having this simplified roller chain size chart with me not only saves me time it also allows me to identify the correct chain easily.

Getting the chain wrong is not just annoying – it will cost money to replace it with the correct one. More importantly, it wastes an engineer’s time and incurs additional costs along with disruption to production schedules caused by the machine’s downtime while the mistake is corrected.

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