worn chains wear cassette teeth, just replacing the chain wont un do the cog wear..
the drive train: chain, rear cluster, and chainrings are "consumables"..

Wearing out is a result of use, and Expected .

Buying KMC * chains their Quick Links can be un done, Shimano opts for a non reusable pin...

But you can use a KMC * link on a shimano chain. the "Speeds " number , chain width has to match..

* German Whipperman also has a Joining link of their own..

12 links , if 1 link = an outer link and an inner link... there is 1" between the 3 pins , of a half inch pitch chain.






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