Heat and vibration can loosen these screws and break the electrical connection. To prevent this, engineers at Marinco Industrial Group, Napa, Calif. (marinco.com), developed Perma-Lock terminals. In this design, the terminal screw tightens down on a contact tang, so the screws exert an upward force on a collar overleaf. This lifting action locks screw threads in place and relieves stress on the terminal. As a result, thermal cycling and vibrations cannot loosen the screws.