A ferrous plate is common on the bottom of Telecaster lead pickups. It is used to help ground the bridge plate and strings and is used to adjust the bridge pickup up or down by the use of three 6/32 machine screws. The elevator plate as it is commonly called is made of steel and is copper plated. The copper plating makes it easier to solder the beginning ground wire and also keep the steel plate from rusting. The steel plate pushes the magnetic field towards the strings where it is needed and can increase the output and brightness in the instrument. On older instruments the elevator plate is put on the pickup after it is potted. When playing at higher volumes the elevator plate can vibrate causing unwanted feedback. To help reduce feedback the bottom plate should be wax potted with the pickup to keep it from vibrating.