Anchor chain size...How Calculated?

[Sinbad1]

I know my anchor chain is 3/8" short link, but what specific component makes this 3/8"

I am assuming that some aspect of each link is 3/8" in measurement, but which part? Or does it relate to something other than the dimension of a part of a link?

 

[VMALLOWS]

It's the diameter of the wire used to make the chain. Now that its generally metric, 8mm converts to 5/16" aprox and 10mm to 3/8".