The three most common steel types are cold rolled steel, galvanneal steel, and galvanized steel. Cold rolled steel, suitable for most interior applications, is uncoated steel with a factory applied coat of primer. Galvannealed (A40) steel is carbon steel coated with an iron-zinc alloy. It provides excellent corrosion protection when combined with a coating of quality prime paint and is adequate for most interior and exterior applications. SDI recommends use of the A Series, both A40 and A60, for primer adhesion. A60 is superior to A40 for inhibiting rust. SDI does not recommend the G series because of inferior primer adhesion properties. Galvanized steel is carbon steel treated with a full zinc alloy. It provides superior rust protection but has poor adhesion properties for prime or finish paint.