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.