(Follow-up to MaplePanda's answer)

Do not confuse the _shift outer cap with long tongue_ (bottom of the first image below) with the _outer cap with short tongue_ (top of the first image).

The _shift outer cap with long tongue_ is used to [weather-proof rear shifting][1] by stopping sand/dust from entering the cable cover.

[![inner and outer][2]][2]

The _outer cap with short tongue_, as you see in an excerpt from a Shimano Dealer's Manual, is the end of the Bowden cable that sits against the brifter.


[![outer cap with short tongue][3]][3]

In addition to having a long or short tongue, another difference is that the outer cap with short tongue has a slant-cut short tongue and a notch that stops it from rotating, to ensure that the slant-cut tongue is properly positioned.



  [1]: https://bicycles.stackexchange.com/q/94907/48599
  [2]: https://i.sstatic.net/55oBLRHO.jpg
  [3]: https://i.sstatic.net/kZvijlgb.jpg