Heavy Core guitar strings are uniquely designed with Dunlop"s proprietary core-to-wrap ratios that are meticulously calculated so the 7-string guitar players can really "dig in" while retaining sound fundamentals. Heavy Core strings (like all of Dunlop"s replacement guitar strings) are manufactured with the highest-quality materials and are engineered for great tone, balance, and feel. "Heavy 7" guitar string gauges: 10-13-17-28-38-48-60