The typical block chain of the 1880's and early 1890's is very heavy. They just didn't know how to make good chains and these chains tend to break at the strangest moments, which can put you into real trouble, going downhill. By making them heavy, they wanted to make the chains safe.
Sizes differ a lot. Standard is de inch pitch chain, but the early manufacturers often produced their own chains, not using any standard. Specially French bikes tend to have other sizes.
I took pictures and size (in millimeters) of my oldest chain and publish it here. This might be a French chain from a Clément bicycle, but I am not 100% sure. It would be interesting to know if anyone can reproduce these chains. But, as I said, the sizes are all a bit different...
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