Length.. Pin center to center, each link is 1/2"... bike chains are all 1/2" pitch.

an inner link + an outer one is 3 pins , so 1". you only cut chains shorter..
if you make it too short* you add a 2nd quick link and a section of new chain

wrap the chain around the 2 biggest chainrings yet? passing thru the RD pulleys..

in the Bike Shop a C /_\ bent piece of an old spoke holds the new chain
gap to try it for length, before finally cutting it.. and fitting the quick link.




* or have a recumbent..



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