D'Addario J71 Pro Arte Ukulele strings are all-nylon, their design inspired and guided by the virtuosity of ukulele artist Jake Shimabukuro. This regular set for tenor ukulele is made from select Pro Art classical guitar string gauges. All D'Addario Pro Art strings are sorted by a sophisticated, computer-controlled, laser machine, which performs diameter/tension measurements and quality checks, ensuring that each set is well-matched, true-sounding and precisely intonated.