Surface oxides

All metal surfaces oxidize in contact with air. This makes it important to fit a cable terminal on a stripped cable for crimping as soon as possible after stripping the cable.

Most cable terminals are tin plated. Tin oxidizes rapidly and the surface oxide coating makes a hard layer on the soft tin which cracks easily when a pin or socket is attached to create a contact.

The surface oxide around contact points protect build a gas tight joint which prevents further oxidation and provides a good electrical contact.