If the key of F tune is written in F, for a piano or keyboard, play it in F. The
easiest solution is to ask the piano player what key he or she is playing, and play in
the pianist's key.
The positions charts recommended in an earlier post will help you to decide which
harp to use. The key of F is located in different positions on different harps, as the
Some of the positions may be out of range for the harp, depending on the tune.
If needed, find a different keyed harp that is easier to play, in a different position.
Some of the positions may be too high or too low for your preferences. If needed,
try another harp.
The key of the harmonica, stamped on the top metal cover, or painted on the comb,
is the "first position" on the harmonica. On a standard 10-hole diatonic harmonica,
the first position key is factory-installed in holes 4-7 only. The holes 1-3 and hole 10
are missing scale notes, by design, to provide chords. The key of F will be found
starting at hole 3 exhale on a Bb harp ("cross harp").
Always look for the easiest key position on the harmonica. If you want to add
improvisations, embellishments, etc., the most commonly used position is second
position. It's sometimes called "cross harp". For example, use a key of Bb harp
in cross position to play the F scale (key of F on a Bb harp).