A side sill plate, also known as a side step or rocker panel, is a component that is installed along the bottom of a car's body, between the front and rear wheels. They are designed to protect the car's body from scratches, dents, and other types of damage caused by rocks, gravel, or other debris on the road. Side sill plates are typically made of stainless steel, aluminum, or plastic and come in various styles and designs to match the car's look and color. They can also enhance the car's appearance by adding a touch of style and elegance to the overall design. Some side sill plates also come with illuminated logos or designs that light up at night for a more custom and sophisticated look.