Originally Posted by
desertdork
The two ends are similarly shaped but sized differently: larger is for Shimano, while the smaller is sized to fit Campagnolo shifters. However, you should be able to use the smaller "Campy" cable end for either brand of shifter without issue.
This is correct. One end should have an "S" molded into the barrel fitting and the other end a "C". Cut off the unneeded end.
As noted Shimano shifters take a slightly larger end fitting than Campy and using the S end in a Campy brifter can cause a jam and difficult removal. I expect using the Campy end in a Shimano shifter won't cause any difficulty but you might as well use the correct one.