Keep loose nuts, screws and other small metal items in reach while under the hood or under the car. Smooth stainless steel trays have powerful ceramic magnets with rubber covers in the base to secure them to a metal toolbox or table. More About Ceramic Magnets: Our hard ceramic ferrite magnets are composed of iron oxide and barium or strontium carbonate. Ceramic magnets exhibit relatively good holding strength for their price, making them a popular choice for many consumer, commercial and technical applications.