Yamaha YHR-567 Owner's Manual page 15

Options
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F Natural Slide (optional)
Attached to the YHR-322's 4th valve slide the F natural slide offers the sound of an open F horn.
It enhances clarity in the mid-low range such as C (actual F) or G (actual C) and stable intonation.
The F Natural Slide is designed so that the horn fits in the case when attached.
F Natural Slide
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