The letter is H for Harmonica
Sometimes known as a mouth organ, the Harmonica is a free wind instrument used notably in the blues, American Folk music, jazz, country and rock and roll.
Although it may seem a simple instrument to those who pick it up and play a simple tune its construction is really quite sophisticated. The varieties of Harmonicas are numerous and it has an interesting history, beginning in Vienna at the beginning of the 19th century.
The music produced by an artist and master of the harmonica is quite spellbinding. Well, to me, anyway, who cannot perceive of making such glorious music with a tongue and puffs of air!
For more interesting takes on H visit here, at ABC Wednesday, with thanks to Roger and Dennis
and all who help.