Gauges 11.5-16-26-41. D"Addario J75 Medium/Heavy Phosphor Bronze Wound Bluegrass Mandolin Strings are acclaimed worldwide for their great, long-lasting tone. Phosphor Bronze was introduced to string making by D"Addario in 1974 and has become synonymous with warm acoustic tone. D"Addario is the world"s largest manufacturer of strings for musical instruments. Many top guitarists won"t play any other brand. Regardless of your playing style, D"Addario has a set of mandolin strings that"s right for you.