Hat shaped endcaps are used to endcap wires and often to splice databusses together on avionic racks.
The tool we use for this is the AMP 48208 crimptool

Here's a few databusses and other wires that were tied together using hat shaped endcaps.

So let's crimp them on some wires.

Stick some wires in the endcap.

And crimp it.

And here's the finished crimp.

Easy right? we use the large opening for the big endcap and the small opening for the small endcap.