Chain and sprocket.

[slappy]

[quote author=slappy link=topic=18685.msg215467#msg215467 date=1446995019]
Remember the good old days when the chain had just a removable link with a clip to hold it in place?

That would indeed make it "the weakest link" and highly unadvisable on a bike capable of high speeds with a heavy chain.
[/quote]

Maybe so but thats how they used to come from the factory as well when I was young.