These tenor ukulele strings are made of Super Nylgut, a new (2014) formulation from Aquila designed to sound like gut strings. This set includes a metal wound 4th string. Low G tuning, GCEA. Maker says the strings have a natural pearl color, a very smooth surface, settle in quickly, and maintain pitch better than previous sets, Aquila also claims this Nylgut is tougher than their prior formulas. No longer includes a Red 4th string.