Stainless Steel Bajo Quinto Strings. Using a heavy core which provides volume and strength, the Stainless steel gives for a longer lasting string and excellent tone projection. Phosphor Bronze are a combination metal alloy of copper-tin phosphor. A very smooth tone with brilliant projection. 80/20 Brass provides a smooth feel with brilliant tone and output. All Bajo Quinto and Bajo Sexto strings come in Ball or Loop End.