[masraum]

OK, I just found the following on the bike barn website.

There are two main chain sizes, 1/2 x 3/32 and 1/2 x 1/8. The 1/2 refers to the distance from pin to pin. The 3/32 and 1/8 refer to the width of the space between the inside sideplates. 1/2 x 3/32 chains are referred to as "derailleur chains" because they're narrow chains for use with bicycles with derailleur gearing. Note: When buying this type of chain be sure to get the one made for the number of cogs on your rear wheel, such as 8-, 9- or 10-speed. The other size chains, 1/2 x 1/8 are referred to as "coaster-brake" or "BMX chains" because they're wider, and for use with coaster-brake, BMX and certain 3-speed drivetrains. If you have any questions about chain compatibility, please contact us.

So it sounds like 1/2x3/32 is standard. And I looked at 3 chains that were listed as 8, 9 and 10 speed chains. Assuming they are all 1/2x3/32, they all also are listed as having 114 links. So the length isn't different. So what is different between them. And, of course, the chain is easy enough to swap. It's just another data point.

It also doesn't seem like the sizes of the cogs vary other than there being more of them. IE, you seem to be able to get 11-32, 11-28, etc... and 50-34 or 50-39-34 seem common regardless of whether it's a Shimano Claris, Sora, Tiagra, 105 or SRAM.