Wikipedia states that it's 5/16" (~7.9mm) while two or three sites list it as 7.75mm.

I'm a little bit confused. Does it differ in different internal width? Does it differ between singlespeed and derailleur chains? If so, I'd like to know the diameter of the derailleur chain's rollers.

  • I don't have any fresh chain to measure, if someone could do the same with fresh new chain that would be an excellent comparison. – Criggie Jun 7 '19 at 22:36

I've measured three well-used chains with vernier calipers. Below are the method and measurements. I'm assuming you mean External diameter of the roller in the chain.

TL,DR 7.66mm +0.04mm -0.02mm measured.

  1. KMC X10 10speed chain with 4223 km 7.64mm enter image description here

  2. Old Shimano CN-HG93 9 speed chain with 3800 km 7.70mm enter image description here

  3. 8 speed folder with cheap Clark chain, around 2000 km 7.64mm enter image description here

Method - my calipers were binding on the inner plates, so to get a good reading I had to make the chain slack and then pull up a roller

BAD enter image description here

GOOD enter image description here

I used an old spoke as a hook to take the tension off while taking that photo.

  • Notice the third caliper photo was taken outside, the difference in lighting is enormous. – Criggie Jun 7 '19 at 22:36
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    Nice. That means that my 2 choices were actually close to what they really are. I was scared that the diameters I got off searching the web were mechinery roller chain sizes, which on their own have a gazillion of different sizes and standards. I just need to see a new chain measure greater than 7.75mm so that I'll use Wikipedia's. – Gregory Leo Jun 8 '19 at 1:53
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    @GregoryLeo as long as its "half-inch pitch" then everything else tends to be right. The only thing that varies then are the width (whether its 1/8" single speed chain or narrower 3/16" derailleur chain and the "speed" of the chain, whether its 5/6-8/9/10/11/12/... speed. And of course there will always be quality variances, cheaper chains are likely to be sloppier. There's a question on the site by RiderX that proved some brand-new chains are over-stretched from new. – Criggie Jun 8 '19 at 1:59
  • @Criggie This looks like a great photographic job you did here. Kudos! – Carel Jun 8 '19 at 13:29

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