An ultra-fine layer of EXP Coating is bonded to the phosphor bronze wrap wire which is then wound onto the hex-shaped core wire. The result is a built-in barrier against the corrosion and wear that can quickly sap the life out of your strings and your sound. EXP coated phosphor bronze mandolin strings have a natural round wound feel and sound fresh and bright with a "new string tone" that lasts three to four times longer than traditional guitar strings. EXP74 Medium - 11, 11, 15, 15, 26, 26, 40, 40. EXP75 Med/Hvy - 11.5, 11.5, 16, 16, 26, 26, 41, 41.