Although cadmium coatings are produced in much less quantity than zinc coatings, they are taken together with zinc coatings as "anodic" coatings. The low contact potential of the cadmium-aluminum couple necessitated the use of cadmium-plated fasteners instead of zinc. Also, since corrosion products do not form solid compounds in the zinc ratio, they are frequently used. Parts that need to be disassembled and reassembled are also cadmium coated. Because cadmium is resistant to alkalis, unlike zinc, parts that come into contact with alkaline cleaners are coated with cadmium.