Check the listing for details. D'Addario H412 Helicore Long Scale Viola D String 17+ Extra Long Scale. Color: 17+ Extra Long Scale, Condition: New. Listed at 17.99 USD. The D'Addario H412 Helicore Viola D String is for instruments with a 16" or longer scale. Helicore strings are justifiably popular. They offer warm, rich sound that's remarkably similar to gut or synthetic core strings. Unlike gut, however, Helicore strings' all-metal construction renders them impervious to fluctuations in humidity and temperature. D'Addario Helicore strings have a multi-strand high-carbon steel core for flexible response and range. The core is overlaid with exotic alloy windings that provide extremely quick bow response and outstanding projection. The end result is a versatile viola string with very long playing life that is extremely stable under all playing conditions.