The NBUKS4 was Ibanez's black nylon ukulele string set, manufactured by Aquila Strings of Italy. It occupied one of two black nylon ukulele string configurations offered under the Ibanez accessory line, positioned for players seeking a distinctive string aesthetic over the more common clear or wound alternatives.

The set was produced by Aquila under their NylBlack designation, using black nylon across all four strings. The gauges ran .024, .032, .037, and .026, covering the full standard four-string ukulele complement. The third string at .037 is the heaviest of the set, with the fourth string returning to a lighter .026 — a characteristic of standard ukulele string ordering.

Owners replacing or matching this set should bring the gauge specifications to a qualified luthier or guitar technician, who can advise on installation tension and tuning stability for their specific ukulele.