The 5 in #35 and #25 Chain

Hi, I’m creating some training presentations and realized that I didn’t know what the chain number was related to. I always correlated the numbers to chain pitch/size both as a student and as a mentor. After reading, it’s fairly obvious that the first digit is the pitch in 1/8s. The 5 is supposed to denote “a bushed chain with no rollers”, but both 25 and #35 chain have rollers (to my knowledge).

Why is this/how can I explain this to students?

Hmmm.
Yeah I just watched a set of videos I found online and I’m as confused as you are. Their site even seems to contradict itself.

This post from 8 years ago may help:

The 5 does mean “rollerless” as in, the chain links use a bushing/pin system rather than a roller.
Here’s a picture of a chain with rollers.

Hope this helps!

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What doesn’t help is that everywhere FRC teams shop online (mcmaster, andymark, wcp…) 25 and 35 are sold as “roller chain”.
Oh well.

Sometimes it’s OK to just shrug and say “I don’t know”.

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The 25 and 35 chains do not have rollers. They only have bushings between the inner plates.

image

The larger ANSI chains have rollers between the inner plates around the OD of the bushings.

image

You can explain it by showing pictures like these.

I don’t have a reference to cite for a reason they are different. However, 25 and 35 chains are intended to be lightweight for lighter loads. Adding rollers around the bushings would make for a heavier chain. The rollers also take up space and would require larger plates, adding even more mass to the chain. For larger loads, where wear can be more of an issue, the rollers can roll when contacting sprocket teeth, possibly reducing wear on both the sprocket and chain. I suppose the tradeoff of increased mass is deemed to be worth it under greater load.

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Some relevant excerpts from ASME B29.1

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