The Delta Blues HD10 harmonica series is diatonic.

Diatonic harmonicas are designed in a specific key, while chromatic harmonicas include every natural and sharp note in a chromatic scale, allowing their players to modulate back and forth between keys. Delta blues music is arguably on of the early types of 'blues' music and is believed to have originated in the Mississippi Delta. Typical instruments used to play the Delta Blues are the acoustic guitar and the harmonica. Early recordings of this music emerged in the late 1920's and, during the depression; the harmonica dominated this sphere of music.The harmonica remains the most portable instrument used in traditional American folk and blues music. Although the earliest harmonicas date to Germany in the mid 19th century, this seemingly simple music instrument has become an icon in American music.With a body that's typically constructed of wood or plastic and a metal cover plate, the harmonica operates by a set of reeds that vibrate when you blow or suck air through any of the 10 holes. Blowing creates one pitch (in a diatonic harmonica 1, 3 and 5 of the scale), while drawing air through the same hole creates another pitch.  The Delta Blues HD10 harmonica series is diatonic.