Yamaha YHR-567 Owner's Manual page 14

Options
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Eb Crook (optional)
This optional main tuning slide is designed for the YHR-314 and transforms the single F horn into
an Eb horn so that you can play Eb parts without transposing.
The crook is designed so that the horn fits in the case when it is attached.
When using the Eb crook, the 1st through 3rd valve
tuning slides should be pulled out a little.
30
Main Tuning Slide
Eb Crook