700C Puerto Rican Cuatro Strings. The Puerto Rican Tres was created from the Cuban Tres. Unlike the Cuban variety, which has a guitar-like shape, the Puerto Rican Tres is shaped like a Puerto Rican Cuatro with cut outs. This 9-string set, with 3 courses, is made of plain steel, silk, and steel with ball ends specifically to take advantage of this intriguing instrument's sonic qualities.