Aquila 16U Tenor Ukulele Low G String – Single New Product at Calido Guitars! Aquila 16U 4th G string tenor ukulele. Nylgut is a synthetic plastic compound that stays in tune with accurate fret intonation. With a density similar to pure gut, Nylgut produces a natural sound and is stable under moisture changes. PRICE: 6.99 Available at CalidoGuitars.com!