Letters often dropped (7)

I believe the answer is:

aitches

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'letters' is the definition.
(aitch is a kind of letter)

I don't understand the rest of the clue.

(Other definitions for aitches that I've seen before include "They are regularly dropped in the East End" , "Two of which are in Hythe" , "Letters" .)

I've seen this clue in The Daily Express.

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