Heavy melting steel (HMS) or heavy melting scrap is broken up into two major categories: HMS 1 and HMS 2, where HMS 1 does not contain galvanized and blackened steel, whereas HMS 2 does. HMS is typically traded as a blend of 1 and 2, either a premium blend (80/20) or lower grade mixes (70/30) and (60/40). For example, HMS 1 and 2 (80/20) should consist of HMS 1 and 2 in the ratio of 80% (HMS 1) and 20% (HMS 2).

Each grade guarantees a minimum piece thickness: at least 1/4 inch (6.3 mm) for HMS 1, and 1/8 in for HMS 2