For nylon string guitar,
                or any guitar with a perfectly flat fretboard.
              2.25 inches, flat.
              It is important to note that almost NO steel string 
                guitars have a truly flat fretboard. Even if your steel string 
                guitar has only a "very slight" curve, it still should 
                use our S1 model.
              But if you play classical, flamenco, or folk guitar 
                with nylon or gut strings, then chances are that your fretboard 
                IS perfectly flat and slightly wider, and the S2 is the capo for 
                you.