ADT Vacuum Suction Cups are used to lift Nonporous materials such as glass, metal, Formica, plastics, fiberglass, linoleum and polished stones. Surfaces should be free of oil, grease or water, otherwise slipping can occur. The grip these suction cups obtain on a load surface is amazingly strong and has to be experienced to be appreciated. Typical use of our vacuum suction cups are for lifting glasses, lifting auto glass, auto windshield and lifting polished granite, marble and other stones. Carrying capacities are listed at a 4:1 safety factor in pounds, which means the suction cups are capable of carrying 4-times as heavy as their listed capacity.