These are aluminum crimps to install on parking brake cables. this is for shortening or making your own cables, usually with cab swaps or frame shortening 

This works with many part numbers, but one example of a common affordable cable is BC3Z2A793P

Use a battery lug crimper to crimp and install these 

8 mm OD
3.5 mm ID
15 mm long 
High quality aluminum that is meant for crimping 

Sold by the pair