Most diatonic harmonicas contain 10 holes, each of which can produce two notes through ordinary blowing or drawing. The holes are referred to primarily by number (1–10), rather than by the notes they produce.
The Blow Notes of the "C" Harmonica
The diagram below shows the 10 numbered holes of the C harmonica with the note that each hole produces when you blow into the hole by exhaling.
The Draw Notes of the "C" Harmonica
The diagram below shows the 10 numbered holes of the C harmonica with the note that each hole produces when you draw air from the hole by inhaling.
Can Diatonic Harmonicas Play More than Seven Notes?
When you use regular blowing and drawing techniques on a diatonic harmonica, it will produce, at most, seven notes of varying pitches. However, it is possible to play all of the notes of the chromatic scale on a diatonic harmonica by using bends (see How to Play Bends on the Harmonica).
How Players Refer to the Different Notes of the Harmonica
Harmonica players won’t just say “play a C,” since that note occurs four times on the instrument. To avoid confusion, harmonica players identify the notes they play first by hole number and then by blow or draw. For instance, a player would refer to the A at the sixth hole as a “hole 6 draw,” to the C at hole 10 as a “hole 10 blow,” and so on. Players often abbreviate this notation by referring to a “6 draw” or a “10 blow.”
The Draw and Blow Notes Together
Together the blow and draw notes of the C harmonica contain all the notes of the C major scale (C–D–E–F–G–A–B–C), the first scale that most beginning harmonica players learn to play.