These aluminium shielding plates are designed to shield the electronics of your Stratocaster from a large amount of induced hum from stray electromagnetic signals.
They create a physical barrier to absorb and shield your electronics from the noise that travels through the pickguard - they then bleed these signals away by sending them to ground. These do not require soldering into your electronics - the physical connection of your potentiometers being affixed to your pickguard should connect them to ground.
Suitable for CTS and other USA sized potentiometer shafts.