D'Addario The EJ65C Concert Ukulele sets is an all-nylon string set inspired and guided by the virtuosity of D'Addario ukulele artist, Jake Shimabukuro. Each string is manufactured on D'Addario's own advanced monofilament extrusion line built exclusively for the production of musical instrument strings. Description Each Custom Extruded Nylon sets are manufactured on D'Addario's own advanced monofilament extrusion line built exclusively for the production of musical instrument strings.